I don't really care who actually made the call but great strategy by Gus to tell Walt he's going to kill Hank. He knew Walt would talk and get word to protect his BIL. This gets Hank off of Gus's back since he'll now be under surveillance. In addition, Gus can now leverage Walt's loose lips as a reason to Jesse why he has to be killed.
This is interesting. If Gus was going to kill Hank, he had no reason to tell Walt he was going to do it. Obviously he knows Walt can't tell Hank directly, but would do as he did, with an anonymous tip.
Doesn't this leave Gus out in the open though? If the tip specified that it was Gus who wanted Hank dead, it stirs up speculation about Gus from the feds again, no? True, it prevents Hank from snooping around anymore, but it could open a much bigger can of worms. Why not just have Hank killed in an "accident" and be done with it?