I have been a contributor on findagrave for years and have fulfilled many photo requests in a large London cemetery.
If there is no plot information on the memorial page there is not much hope of finding the grave, though I did once find one by accident because it was an unusual surname and I thought I remembered seeing that surname in the photo request list for the cemetery so I photographed the grave. When I got home I was pleased to find that my photo matched the request.
There is a plot field on the memorial page but sometimes people put the plot information in the note that accompanies the request, or elsewhere on the memorial page, so I always check.
There is no obligation on volunteers to get plot information or do anything they don't want to. Some councils charge for looking up plot details, and some will only give information to relatives.
Deleted users won't get notified if their photo requests are fulfilled, but you would still get Volunteer Photo Credit on your profile, so it is up to you if you want to bother with those. Findagrave memorials get picked up as hints on familysearch and Ancestry so the requester may see your photos one day.
Hope I've answered all your questions. If you want to know anything else, I will be happy to help.
I don't just fulfil requests, I photograph as many graves as I can and make memorial pages for them. Graving is a great hobby, don't know how I would have got through lockdown without it.