Thanks for all the input.
For some reason, I never would have thought of the gryehound/whippet angle. (Probably as he's coming from a Beagle and Dalmation Rescue - who also have lots of other breeds). I've 'googled' a few of the mixes and they all look pretty similar. Guess I'll never know! (Unless I get that DNA test - but so far, it hasn't come to that!)
We adopted his 100% hound 'kennel' mate last year, and I'm thinking long and hard about a second dog. Both were suggested to us for their quiet, calm nature (and we know they get along!). However, I've had some challenges training our first real hound dog, so I was hoping that this guy is more 'non-hound' than hound... (According to the Rescue, he acts more "non-hound"). Guess I'll have to find out!