There are 6 verses APPARENTLY admonishing homosexual sexual acts (not necessarily homosexuals), and over 300 against acts by heterosexuals - the use of any position aside from Missionary for examples. You don't ask all hetero clergy to follow it all.
The first two you mention are about RAPE - not homosexuality - rape is about POWER over someone else - and as you can see in Judges, they don't care what gender they are, given they raped the concubine.
Leviticus, like all verses, needs it's social, cultural and history context with it - rather than cherry picking. In Lev - they are trying to forge an existence in the desert - best way to increase the population is outlaw non-reproductive sex in the best way possible - punish it by death. Lev includes a LOT of instructions to do with heterosexuals as well - I don't see anyone INSISTING they follow those. Or the food rules (designed to stop food poisioning etc).
Romans - Paul trying to turn people away from Pagan faiths by denoucing the more...enjoyable...parts of their rituals.
Corinthians - translations of two words used by Paul that do not actually mean homosexual - one means effeminate (and hell, there are a lot of effeminate metrosexual straight men), and the other means soft. These verses are referring to the temple prositutes, and those who were given to the leaders/ (?gods...) of the time, and where not to be used by anyone else.
Timothy - if you managed to get a Bible with the word Homosexual in it - take it back. Translation bias sucks. The word itself didn't exist until the early 1900s. If you meant "Sodomite" - doesn't necessarily mean homosexual - plenty of heterosexuals practice anal. This verse I don't know as well as the others, sorry.
So, how can a clergyman be gay? Because none of these verses say that they can't. It merely says that they shouldn't partake in the acts - in the OLD Testament - yet, we'll let clergy wear mixed fabrics, eat pork, cut their hair, trim their beards, have sex with their wifes in positions other than missionary, touch their wifes when their wifes are menstruating. Why? Because NONE of us follow Leviticus any more, since the NT.
The New Testament verses are against the Pagan community, not necessarily homosexual either. They also don't prescribe the "qualities" of Clergy.
If there are gay clergy, they are obviously of a church who feels that they are just as qualified to do the job. Not one of us is without sin.