Wow, thank you, I learned something researching this!

Yes they can mine alternate coin, but only if it uses the same SHA256 algorhitm as BTC. So LTC, no, bytecoin yes.

And that is a busy thread https://bitcointalk.org/index.php?topic=164569.0

But here's what I learned. Any ALT coin using SHA256 is at risk of the 51% attack (or some similar brute force attack) due to the power of the larger  ASIC's over any initial nethash. So do you trust your ALT coin now? I shall read more on this, thanks.