Blood donations by MSMs: Legal from Sep 23, 1932 to now.
They don't ask people if they're gay or not when you are about to donate blood, you just donate as any other human being, unless you don't mention having sex with same gender or any kind of sex you'll be fine.
While Saudi Arabia has no specific law banning homosexuality, it does use Sharia law as a framework. Punishment for those who are convicted varies between flogging and imprisonment.
Those who are convicted twice face an automatic execution. Under Saudi Arabian interpretation of Sharia, a Non Muslim male who engages sexual relations with a Muslim male could face the Capital Punishment , married men who have sex with another men could also face execution by stoning for the offense of adultery . While sex between Muslim men is is sentenced by Flogging on the first offence. Second conviction merits execution.