I added the tag for EuroAristo to your question. I also found that there was another duplicate, Meriadoc-5 so those should be merged as well. That profile actually have a description of whom the profile is representing, it is always good to search for duplicates before, sometimes spare you the time of research and putting together a bio.
As to your original question, I don't think you should need to contact the managers of this profile before writing a biography of someone said to have existed that long ago when there really is not that much info on the profile anyway.
I try to use common sense, if the manager active and have put a lot of work on a profile, then of course I communicate if I would like to do some additional work on the profile or I add the sources I have found in a comment on the profile for the manager to check out and add.
Sometime I add what info and source I have found in the bio and then send a message to the manager that I found additional info and they might want to rewrite it to fit their "style" of bio. If they still have interest in WT and their profile they usually check it out and if they have lost interest then the profile is at least sourced and have some info on it.
If I only want to add a source for a birthdate then I might add the source without communicating as I am not really changing anything, just adding a source to the profile.
I could add that I mainly work profiles in the area I have knowledge of (Sweden) and mostly rely on images of original church books as sources.