I think it’s a question of relevance to iNat, and not usefulness which, as others have said, is a bit hard to judge.
iNat is really for observations of extant taxa, it’s not a place for posting observations of fossils. This is not a value judgement of fossils or fossil records, of course (they’re cool! and important!) but iNat observations should be of encounters with recent evidence of organisms (and the vast majority of those obesrvations should be of wild organisms). FWIW, fossils have been discussed multiple times in the forum:
https://forum.inaturalist.org/t/identifying-fossils/11271
https://forum.inaturalist.org/t/uploading-prehistoric-fossils/13457
https://forum.inaturalist.org/t/rock-fossil-crystal-inat/24333
I’d suggest using a different, fossil-focused platform and refrain from encouraging people to post more observations of fossils to iNat because it’s just not the place for them. But a traditional project that people can put existing fossil observations into seems OK.