Pon Farr is, at least according to one source, a natural urge to procreate felt by heterosexual Vulcans. We see at least one instance in the EU where a gay male Vulcan is stated not to feel that urge.
"That reminds me... how is your 'friend,' Sotok? Are you and he still together?"
"On and off... at the moment, off, but eventually, on, I would suspect. He is well... much to the annoyance of Father. He still believes that, were it not for my involvement with Sotok, my 'true' nature would have presented itself, and the pon farr urges would have swept me up in their inevitable tide of reproductive drive."
Star Trek - New Frontier 10: Excalibur: Renaissance
and
"And do you, Slon, have a mate to whom you were driven by pon farr?"
"No." Slon looked down at his empty hands, and it was the first time Burgoyne realized that he wasn't holding a drink. "No ... I do not."
"Well... shouldn't you be due for that?"
"That is ... apparently not going to occur in my case."
"Really? Why not?"
Slon looked at hir steadily. "I have a lack of interest in reproduction that no amount of genetic tradition can overcome."
It stands to reason that this instinctual reproductive urge can only be quelled (at least in any normal manner) by mating repeatedly with someone of the opposite sex. That being said, this being Star Trek we can presumably add the usual caveats about female-looking gender-neutrals, female-looking holograms, etc.
We also don't know whether a lesbian Vulcan would feel the urge to mate with a male. One assumes that if they were interested in having a child, their urge would be to procreate (with a male), regardless of their normally asserted sexual preference.
It follows that a heterosexual Vulcan mating with someone of the same sex would not result in the pon farr being sated, in the same way that Vorik's pon farr was not satisfied with mating with a mate that he found unsuitable. The issue would not apply to a homosexual Vulcan as they wouldn't feel the pon farr in the first place.
