Mixing HBAs in a failover cluster?

I have a two server failover cluster, and for various reasons - they're on mismatched hardware.

One has Emulex HBAs installed, the other Qlogic.

I'd be twitchy about using two different makes/models of card for multipathing within a box. I'm therefore a bit uncomfortable doing it in a shared storage failover cluster.

Is there a particular reason why this might be a bad (or good?) idea, or am I just being unduly concerned?

You don't really mention enough detail at all but I'd have zero concerns about mixing Emulex and QLogic - in fact in our highest-availability systems I consciously do this kind of thing, even with Ethernet ports. The reason being that if the driver for one manufacturer's card suddenly dies or develops a bug then the other driver should carry on in many cases.

So no, I'd not be worried and so long as you get the latest drivers I actually think it's a good thing.