I have played with Rambolo a lot, and spectated him while he did longjumps for many hours over the course of the last few months, as well as practiced with him in a private longjump server for a good while.  I've watched many of his jumps slowed down, and seen his flight coordinates graphed out.  He has been willing to do anything asked of him to show that he doesn't cheat, and it's pretty well accepted now that he is just the best at this time.

With all of that being the case, I am yet to see any legitimate reason to suspect him of cheating in any way.  There is no way to say for certain if ANY player is cheating or not, and I'm sure there are cheaters all throughout kreedz mod.  However, I see no reason to suspect Rambolo any more than any other player.  In fact, I suspect several other players of cheating far more, and find no reason to consider Rambolo's accomplishments and skills illegitimate.   If he is cheating, he would likely be the best in the world at hiding it, because with eyes watching him constantly when he plays for months, it would only make sense for someone to have concrete evidence against him by now.

Regarding his VAC ban, VAC bans aren't necessarily conclusive proof of cheating.  People receive VAC bans frequently for unknown reasons, and with how uncooperative Steam support tends to be, many are unable to have the situation resolved ideally.  Even if the VAC ban was for cheating, we have no idea what game that would have come from, and VAC is highly unlikely to pick up any hacks for KZ.

I understand the natural tendency to suspect anybody who largely exceeds the ability of the next best players, but the fact of the matter is that even at his current record of 290 units, he probably is not pushing longjumping in CSGO as high as it can be quite yet.  I suspect that the actual maximums that anybody will attain in the life of CSGO KZ will be around 293 with the bind and 286 without it.  In a few more months, there will probably be several players on the level that Rambolo is at now.

Once again, I can not confirm with 100 percent certainty that any player is not cheating.  That being said, nobody has yet been able to confirm with any measure of certainty that Rambolo cheats.  In my opinion it is unfair to tarnish a player's reputation with no real evidence.