I've wondered this myself, but more generically than just Ciscos and ASAs.
I did this with Barracudas when I demo'ed them a few years ago. The Barracuda each had their own self signed cert, and you imported their public key portion into the remote side for authentication.
I'm not sure how it would work if both sides are using the same wildcard cert - I would think you would loose a large part of the security.