I know it might squirm a bit, but with a tube and pressures above say 30psi – would it be ok to run on the front?

Or on a Mavic 717?

I'm looking for something a bit wider than an Advantage 2.25. I have a High Roller 2.35 which is narrower than the Advantage…so suppose I'm trying to find something a bit bigger but probably not a proper 2.5?

Are WTB Prowler 2.5's particularly wide? (they're cheap on CRC at the mo)

The official answer is no, but if you're going to run higher tyre pressures, then it's still no.
Max tyre size for those rims is quoted as 2.1 so you can get away with 2.3 but not much more.

I think the more relevant answer is why would you want to? The suggestion being that if you 'need' a 2.5" tyre then perhaps the Olympic rim is not the right wheel for god riding.
A 2.35 dual ply high roller for example can happily be used for full on dh use so the need for something with more volume would suggest you're riding very rocky and fast terrain that warrants the higher volume.
What is it you're trying to achieve? Perhaps there is a tyre that will fit and do the job.

it will work but it will squirm like crazy.

I tried a 2.3 racing ralph and it was not happy.

I use 2.1 sb8 or speed kings 2.3 – which are like 2.1s elsewhere – normally and they are great on olympics.