do 3.8 skins/themes work on 3.7 boards?
 

??...

I never heard of vBulletin 3.7 or 3.8 existing yet :p
At the moment there's vBulletin 3.0, 3.5 and 3.6 in the 3.x branch. Styles for an older branch doesn't have actual templates if they aren't using the default ones. This can affect some features and of course never features aren't integrated in the old templates yet (if they aren't using the default ones). In the worst case, there can be a security issue. If you have some vBulletin knowledge, you can update the templates yourself.

I assume the OP means 3.6.7 and 3.6.8

yea ^thats what i meant. my bad.

i am using 3.6.7 skins on 3.6.8 install w/ out issue. i think most of the differences are related to blog hooks.

i'm reffering to the opposite though. 3.6.8 on 3.6.7. maybe it works the way you are doing it. i want to know if it works the other way though :(

The changes between 3.6.7 & 3.6.8 templates are listed in the 3.6.8 release thread on vbulletin.com, off-hand I can't remember anything that would cause any major issues.