Unless the crab has another secret weapon that has not been mentioned, it's not possible for it to grab Blitz Juggernaut's leg. As specified in two posts, the Vanguard is forcing the claw away from it using its free forearm. Dazza has specifically fought to get the crab dead to rights.

I don't mind the acid blood, but any acid that can do more than surface damage on a heavily armored mech would be strong enough to melt the kaiju from the inside, or damage the kaiju as well as soon as a blood vessel is ruptured, which incidentally just happened. That being said, damaging the paintwork is liable to piss the Australian off, which could have its own repercussions.