Have a look at the Rules (Tab at top of page).
If its not mentioned there's a fair chance its OK. The Commercial
Post ones are a bit intimidating, but if you're not selling anything and its not your site then well, I don't know. Should be OK...
We have not, to the best of my knowledge, experienced any problems with YouTube links.
As with all posts I recommend using the "Preview" button to check how it all looks before clicking "Submit Reply".