Not sure about his kickboxing history, if its professional or not, but I know the kumite used to be pretty hardcore back then, even ending in knockouts, though I am not interested in this topic enough to look at who he might have knocked out or how europe had their kumites back then (though someone on some other site said he knocked out a list of people which can be verified by your own research).
Any why are people quoting me like I'm supporting him in being a good fighter, lol?
I consider JCVD the real thing because he has a black belt, has competed in sport karate to some extent, and does have video of him doing kickboxing (might be promotional though he looks kind of.... fruity, he seems to be showing off while his partner is being serious, and this was before he made movies and was a promo for a world championship full contact fight), where other ma actors dont compete in anything and just jump into acting with minimal ma experience.
Also, its not so uncommon to go from kumite to kickboxing, boxing was being mixed in karate for years, and that resulted in pro-karate, full contact, etc.