I've heard that before.
But in my opinion it's not true. hide was pretty, delicate, skinny, wore make-up, bright clothes and stuff that a lot of women would wear.
And plus, the fact that he would never undress (show bare arms, legs, chest...) in public might lead some people to question his gender.
But I don't think that would make him a transgender.
Anyway, if Yoshiki had never cut his hair and if he wasn't constantly nude in photoshoots I'd also say he could be a woman.