Yes, you can block them: https://forum.inaturalist.org/t/some-updates-to-blocking-and-muting/39866
Update: I hadn’t used muting or blocking on iNat, but just tested and it seems that to remove someone’s observations from your Identification feed, you need to block, not just mute. I’ve changed the word above from “mute” to “block”.
Second update: I agree that this is not really what the block feature is for. If the mute function removed the observations from your Identify feed it would seem appropriate, as was my initial suggestion, but it doesn’t seem to work like that.