I will ask Steve to confirm this but as far as I am aware the answer is, as you suspect, no. Short of actually disallowing guests access to the forum your poll happens to be using which is probably a bit drastic.

I dont think there is any special logic there regarding guests…  but cannot remember if poll hiding is only from users who can vote… if guests cannot vote, that would explain it, but would need to check

No, actually, poll results should be hidden from everyone…  just ran some tests and its working fine for me… poll results even hidden from guests…  so cannot duplicate… perhaps you can explain further and pass along some of your other polls settings (ie logging method, max votes, etc)…

remember you have to set the hide results on a poll by poll basis… the option in admin just enables you to hide results when creating the poll (much better than all or none on hiding)…

Strange I cannot replicate it with another poll… is working fine.  

yes, odd…  well, let us know if it happens again…