Yes, it is ok as long as both don't appear on the same page... But Bidvertiser is worth nothing or almost... :/
But make sure that the Bidvertiser ads do not use the similar ad format or color schemes with the existing adsense ads.
It's not worth doing. You put yourself into a very risky situation. I haven't had much success with Bidvertister, yet I continue to have a huge amount of success with Adsense. If it were me, wouldn't rick it just to score a few more bucks.
I tried placing Bidvertiser ads on the same page as my Adsense adds once, and from then on I only made about 2 cents when someone clicked on the Adsense ads on my site. I guess I had both ads looking too similar or something. I wouldn't recommend combining both ads on the same page.