I've been trying to locate the Sanborn's Fire Insurance Maps for Seattle, Washington to answer what structured were located in the industrial areas of 6th Ave. South. As you know, 6th Ave. changes to 6th Ave. South once it goes past Yesler. In the area just west of the "International District" and before 1942 Nihonmachi or the Japanese district, there was a large "Hooverville" or extemporized migrant encampment in the area of the railroads near the Kingdome, since torn down.
That is too far north for 6th Ave. S. unfortunately. The Library of Congress does not seem to have the maps digitized, but perhaps one of the Universities like UW has them at one of the libraries?
You also might see if there was some kind of King County inquest? Sometimes when a deceased person was found, particularly in this case, a man who may have ingested some type of poison/poisonous alcohol, etc.? The King County Clerk might have information about how to locate inquests from that time period.
Puget Sound Regional Archives
3000 Landerholm Circle SE
Bellevue, WA 98007
Good luck! Historically there was a "skid row" along Yesler.
I hope you can find more details about your missing ancestor, and whether or not this unfortunate decedent is your ancestor.