Bitmessage isn't blockchain based. Bitmessage, at the moment, is entirely separate from Bitcoin. While in Bitcoin, every full node has a complete transaction history since the network's inception, Bitmessage nodes simply hold every message since 2.5 days ago.
Assuming that the hash function does not need to be changed for some reason, of course. That is part of the risk of using hardware crypto: a vulnerability in the cryptosystem is expensive to fix.
My mining pools just throws in namecoins for me. I guess they can check the same hash against both systems.