I don’t think it’s as clear cut as saying they are not infertile because they are two men @HermioneKipper (putting the ethics of surrogacy to one side for a minute).
Yes they are two men and therefore biologically incapable of having a child together, and yes they aren’t both medically infertile (unless one of them is) because they could hypothetically go off and have a child in a relationship with a woman. But they can’t do this because they are gay, and also because they’ve chosen to be together and not with anyone else.
In the majority of straight couples that have problems conceiving and get access to fertility treatment, only one of the two will have a fertility issue. (Yes there will be some couples where both do, but for the majority the medical problem will be with one person). The other person is technically not medically infertile because they could go off and have a child with another man / woman. But no doctor or health service nowadays would say to a woman, we’re not giving you and your husband IUI or IVF because you’re fertile, the problem is with your husbands low sperm motility, so what you need to do is just go off have a child with another man. The couple is considered to have fertility problems, regardless of the fact that one of them could probably have a child without assistance, with someone else.
I largely disagree with surrogacy in all but the most altruistic of cases, although I also do feel for people who long for a biological child and can’t have one. It’s a thorny and difficult issue.
But surrogacy aside, I don’t think it’s quite right to say. They aren’t infertile because they are two gay men and technically have no medical reason why they can’t have a child.