No, he just says “I can’t move against Grindelwald.” It’s not until the end when Newt hands him the blood pact that he acknowledges it’s existence to another person, and even then he only (vaguely, cryptically) replies “maybe” as to whether or not he can destroy it. Remember Dumbledore admitted he put off facing Grindelwald until it was “embarrassing” not to do so—that object is not the only thing preventing him from fighting him. It’s a major part, but not the sole reason.

A blood pact is not an unbreakable vow. I imagine the brilliant teenagers knew about the unbreakable vow, but decided on a blood pact as a better gesture of their relationship—in the same way an engagement ring is a sweet promise because you don’t agree to die if the relationship ends.

Someone else made an allegory as to how blood pacts vs. unbreakable vows (could) work: an unbreakable vow kills you if you break the promise, but allows you to do it, while a blood pact has a magical force that prevents you from breaking the promise. Like, if I tried to eat something I made a blood pact not to, it’d get shoved out of my mouth.