As for Haider's gayness: yes, it is relevant. Firstly, there is the usual notion that somebody's sexuality is relevant for politicians who portray themselves as conservative family man. Haider lived two lives:

Haider, who voted against a parliamentary motion to lower the age of consent for homosexuals, had presented himself as a family man who drank sparingly. But after the car crash it was revealed that he had been driving at twice the speed limit, his blood alcohol level had been four times the legal limit, and he had spent his final hours in a gay bar in Klagenfurt (Link from Ronin's post above)

Secondly, it is important since this is Austria. A cocaine sniffing pederast nazi provocateur, that is exactly what Haider was. And he was this because he was Austrian. I think I'll do more than just insult Haider. I'll take some swipes at the whole of Austria:
Austria has never come to terms with its nazi past. Much less so than Germany. Austria was not de-nazified like Germany was after WWII. The nazi period was seen as a foreign invasion, an alien aborration of Austria's history. This couldn't be farther from the truth. Nazism has many roots, but certainly Austria's history is among the foremost of them. Nazism is better described as Austro-Balkan nationalism that invaded Germany at a time when Germany was confused and bitter.
Austria has not engaged in some self-criticism. In taking a long, hard look into what made Austria a nazi hotbed, and how this could be prevented.

Behind the tidy, bourgeois façades of Austria - upheld externally and domestically, individually and collectively - something always brews. Be it the rape cellars of family men, secretly gay politicians who vote anti-gay laws, widespread nazi-sympathies from businessmen, perennial anti-Semitism in intellectual powerhouse Vienna, or hatred of Slavs in precisely the Austrian provinces that are inhabited by Germanised Slavs. No wonder Freud was a product of Austria.

That is Austria. And Haider, his complicated character and policies, and his popularity at home, are the unique products of Austria.