It may not be specifically forbidden in the unspoken Big 4 playbook but I believe it is assumed that firms consider other firms' LinkedIn groups off limits when it comes to spamming for candidates.
This guy at EY did not get the memo:
Now, the video isn't just an informative short film on, say, ethics or the value of IFRS CPE you'll never use. Nope. It's about building your career in the FAAS practice at EY. Xavier, WTF are you doing, bro?!
Either this guy is not terribly bright or a master genius, we'll leave that up to you to decide.