I've always pronounced Biollante as "Bio - lan - tay" : with 'Bio' as in biology and the 'A' prounced similar to the 'a' in lawn or pawn.
I'm not consistant with Hedorah. Sometimes I'll notice myself saying it like "He - door - ah" and other times like "Hea - door - ah" {the 'hea' said like the 'hea' portion of head}.
On a similar note? Anguirus what's the correct pronounciation? I generally say it something like "Ang - gear - us".