I have no plans to add another dog for quite a few years but can't help wondering would another entire male live with my entire male alright or is an unspayed female a better option bearing in mind that i can keep them separately when she is in season.

I have too entire males living together. They were introduced at 18 and 4 months on neutral ground, we've never had a cross word yet and they're 2 and 3.5 now!

Either would probably fit in very well with your greyhounds. I've often brought adult males into the house with my existing adult borzoi males, 2 who were stud dogs too, with no problems whatsoever. Hounds are pack animals and generally tolerate their own type very well.

Yes I had hoped as much from all positive experiences of any entire dog of either gender we took in from kennels for homing however that was the opposite way around - bringing a dog into the home of two neutered dogs. But hey how would all the hounds have lived together long, long ago if it didn't work :) I hope to add to the gang in a few years so nice to know i won't necessarily be limited in choosing gender as i prefer boys a bit!