I suppose it depends on what you get out of spanking; how you feel about spanking; weather or not you strictly separate spanking from eroticism and / or whether or not you have any erotic feelings for (or also for) the same gender.
In my personal experience spanking - including punishment spankings - is
always erotic. And if I actually am bi sexual (allegedly we all are) it is buried very deep, so for me spanking another man would not be very enjoyable. By the same token when looking at spanking-porn pics two women never do it for me unless both women are spanked by a man. And lastly since I have a dominant personality, for me it needs to be men spanking women (although I still occasionally allow my wife to spank me if I did something real stupid - fair is fair, I would also spank her for it)
My wife is very compatible with me in all of these aspects. For both of us adult spanking, even if for punishment, is always erotic. The punishment is the pain, it doesn\'t mean we can\'t get horny while we are at it
So my wife is likely to dress up when she has to appear for a spanking and even when I really let her have it there is always also some flirting going on.
Similarly, because of the sexual nature of spanking in our family, it also stays in the family... i.e. no spanking or getting spanked by someone else.
So for me spanking another man is out. But I always believe, as long as the wife and I can do
our thing, everyone else should be allowed to do
their thing. The only limitations to that are that everyone involved is an adult and participates in it voluntarily. So for any man thinking of spanking another man... it really is up to you and that other man whether or not you want to go ahead with it. And as other posters have pointed out spanking does not have to be erotic, so sexual preferences do not have to play a role in making the choice either.