Yes you can as far as they don't look exactly like AdSense. Running a lot of advertisements is not a good idea though. You won't make much more money. Chikita id not paying very well, some goes for AdBrite. Not sure about Kontera. I would suggest you to stay with AdSense and just optimize the placement / colors, etc.
Kontera inline ads are good but sometimes the ads display real slow. CJ can be a great way to make money in addition to adsense.
how long does it takes for Kontera ads to appear. I just applied with them and I put the code and it didn't appear on my site so I removed it. I don't have a lot of content on my site so I fill them up with ads. My audience are only there for my stock picks which I update daily.