I'm pretty sure I know the answer to this already, but i figured I'd ask just to be sure.

Widow's Watch reads, in pertinent part, "Response: After you play a unique card from your hand, kneel Widow's Watch or kneel a Learned character to search your deck for a copy of that card, reveal it, and add it back to your hand. Then, shuffle your deck. "

Since Ambush "puts into play" Widow's Watch can't be triggered off of unique cards that were ambushed in, correct?

Thanks folks!

You are correct. Play and put into play are two very different things.