I just did some searching on the adsense help forum. It looks like there is no definite answer there as well. I believe the general consenus is as long as the Kontera ad color / look is different than the adsense ads, it is okay.
I got the standard message back from Google Support when asking about Kontera and Adsense on the same page. I then replied back: "Hi,
Thanks for the reply. I just want to confirm- If my Adsense ads are all
black, and I make my Kontera ads blue (to distingush the two), this is
okay."
Here is what Google wrote back: Hi,
As long as users can distinguish between the two ads, this would be
acceptable.