This unknown Mr. Gomersheimer was the first husband of Anna Elisabeth, father of Michael Gomersheimer. There were no people in Grimm with that surname. I'm in the process of checking other Volga German villages to see if I can find him or a possible parent.
While going through the 1767 Census Index, I found a Johann Heinrich Boehmersheim in Warenburg, band 4, page 323. This seems to be a real possibility as a match for his surname. Look at the two names written next to each other.
The letters B and G sound similar, and with a longer name like this, it's easy to understand how the census taker may have incorrectly written down what he thought he heard. Johann Heinrich Boehmersheim could have been this man's father, or he may have had sons old enough to be his father. I checked the 1798 Census of the German Colonies Along the Volga and there were no remaining Boehmersheims in any of the colonies. They may have shortened the name to Boehmer or Boehm. Complicating this search is the fact that the original name in Germany appears to have been spelled Bommersheim, or some shortened version of this alternate name. The umlaut and the H seem to be new introductions to the spelling.
This unknown male Gomersheimer / Boehmersheim is not specifically listed in the 1834 census, but his son Michael is.
Here is one example of a record with the alternate spelling of the surname. 
I looked up Bellersheim on a map; it can be found at these coordinates:
It is north of Frankfurt by about 37 miles, 56 miles from Darmstadt, and offers the compelling village with a similar sounding name: Bellersheim.   This record was noted here only to show the alternate spelling of the name and the similar village name. He is not a match for the Johann Heinrich Boehmersheim who immigrated to Russia and settled in Warenburg.
According to the Kulberg Reports, Johann Heinrich Boehmersheim was a weaver from Darmstadt.  He traveled to Oranienbaum with his wife Anna Sophia and five children:
If Johann Heinrich was 20 when his first child was born, and that child was 20 in 1766, then Johann Heinrich Boehmersheim was born around 1726. This makes him about 41 or older at the time he and his family immigrated to Russia.
The family departed from Luebeck on the ship called Die Vergelte Weintraube with their recruiter Le Roy, arriving in Oranienbaum on 15 June 1766. After arriving in Oranienbaum, new German immigrants were processed, took an oath of allegiance to their new country, and usually spent about nine months to a year in temporary quarters until the following spring when frozen rivers melted and it was slightly less treacherous to begin their journey to the Volga River. Many people did not survive that first winter in Oranienbaum, and still more perished on the journey to their new home.
Journey to Warenburg
The village of Warenburg was founded as a Lutheran colony on 12 May 1767 by Le Roy and another recruiter with former residents from Brandenburg, Darmstadt, Holstein, Prussia, and Württemberg. These new residents were recorded in what is loosely called the Volga German Transport List.  Interestingly, none of these Boehmersheim family members appear in this list, which seems odd since they are mentioned in the Kulberg Reports.
That said, if his wife and children became ill, some of them even dying, his journey to Warenburg may have been delayed and he may have tagged along with another group without his name being officially added to the transport list.
1767 Warenburg Census 
To recap, at some point between his arrival in Oranienbaum and his arrival in Warenburg, Johann Heinrich's wife died. Before the first census was taken in the latter part of 1767, he had remarried Elisabeth Margaretha. Although there is no reference to her age in the 1767 census, she would have had to be young enough to be able to bear children. There were no children living with the couple at the time of that census.
This means that at some point after the census, the couple had to have at least one child, a boy, estimated to have been born around 1780. It could have been earlier.
That boy grew up to marry a woman named Anna Elisabeth who may have been from Warenburg or Grimm. They had a son, Michael, in 1808. After the death of Mr. Boehmersheim before 1814, she remarried Johann Philipp Schott from Grimm. Their first child, a son, was born in 1815. Interestingly, they named him Johann Heinrich, perhaps after her first husband or former father-in-law. It's difficult to say that with any certainty since the pool of names Volga Germans used was quite limited, but it is interesting to consider.
There are no Böhmersheims in the 1798 census in Warenburg or in any other Volga German village. 
I have sent a note to the Warenburg village coordinator to see if I can find out more about the Boehmersheim family from the 1775 census. It may reveal the name of Anna Elisabeth's first husband.
The village coordinators for Warenburg are listed below.
13 January 2019 Update
Heard back from Sharon White. There is no 1775 Warenburg census. The only records available for that time frame besides the 1767 and 1798 census records are birth records for 1795 to 1811. AHSGR has not purchased them yet. Miller-33353 03:02, 14 January 2019 (UTC)
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