FCP7 Works fine but I didn’t like having to connect to my viewing monitor using the decklink card instead using it as an extended monitor.
You have to constantly change the Blackmagic output settings whenever your sequence settings change instead of just setting output to “Preview” for everything. Also, I liked taking full screen screenshots in FCP and couldn’t after connecting through the decklink card.
You can still connect if you have a third monitor for scopes, which I do, but it was a cheap monitor. In the end I switch the cables when working with FCP and Resolve. I prefer to connect to my viewing/grading monitor using “preview” over the decklink card when editing in FCP.
But in direct answer to your question. I have never had a problem running FCP and 2 cards.