As has been proven by other companies recently, so long as there is a "catchall" clause in the terms, anything you do has the potential to be against their terms.

All you can ever really do is hope to not be caught up in something Google (or its bots) considers "bad".

EDIT: A few catchall terms from YouTube's TOS:

"YouTube may, in its sole discretion, modify or revise these Terms of Service and policies at any time, and you agree to be bound by such modifications or revisions."

"You agree not to access Content through any technology or means other than the video playback pages of the Service itself, the Embeddable Player, or other explicitly authorized means YouTube may designate." (There go all New Pipe accounts)

"YouTube reserves the right to discontinue any aspect of the Service at any time."

"YouTube reserves the right to decide whether Content violates these Terms of Service for reasons other than copyright infringement, [...]. YouTube may at any time, without prior notice and in its sole discretion, [...] terminate a user's account for submitting such material in violation of these Terms of Service."