I don’t think so. You can add multiple Syncthing folders for any given on disk directory (with different settings), but the ignore list lives in that directory so it becomes shared.
I’d also mention that in this hypothetical scenario, your clients could edit their own ignore lists and then access all of the files which may be undesirable.
It is a possible approach. The problem is that I do not trust those clients to have full access to the hosted folder and let them manage the ignore lists.