This is allowed and acceptable under both of their terms of services.
Chitika has even gone a further step and disabled their contextual mode by default.
You can display both, only if Chitika eMiniMalls is in non-contextual mode. If you have Chitika eMiniMalls in contextual mode, then you can’t. Google Adsense does not allow other ad networks [...]

There currently is no limit or restrictions to how many you place on a page.
Chitika does suggest 3-4 to retain a high CTR, but that’s dependant on your page.

Chitika has very advanced fraud detection scripts in place.
Even clicking your own ads by mistake is automatically resolved.
This is the large (Besides the visual and functional) difference between Chitika and Google Adsense. Adsense is an ongoing audit, potentially, each click you receive is audited. Whereas with Chitika auditing occurs at the end of the month.
Multiple [...]

This ony works in non-contextual mode, which is the default for Chitika eMiniMalls
Generate your code

<script type=”text/javascript”><!–
ch_client = “Your Login”;
ch_width = 728;
ch_height = 90;
ch_non_contextual = 1;
var ch_queries = new Array( “digital cameras”, “stereo”, “sony playstation”, “dell laptop” );
var ch_selected=Math.floor((Math.random()*ch_queries.length));
ch_query = ch_queries[ch_selected];//–></script>
<script  src=”http://scripts.chitika.net/eminimalls/mm.js” type=”text/javascript”>
</script>

Place this under the bolded code
ch_sid = ch_query;

var ch_queries = new Array( “digital cameras”, “stereo”, [...]

Slim Down the Width of your Forum
How wide is your forum? Is it set to 100%? You’ll most likely see an increase by using a pixel width to limit how large your forum stretches.
759px wide is a good length. This makes larger posts look more column-like and easier to read. As well your ads mesh [...]

Percentage of click locations on a forum case study
50-60% After the last post in a thread
30-35% After the first post in a thread
10-25% Under the forum index, above the forum listing

In vBulletin go in to you Admin Control Panel then Styles and Templates then Style Manager then double click on Postbit Templates then either Postbit or Posbit_Legacy, depending on which one you are using (Legacy is the one with the avatar and user data horizontal to the post)
To place a Chitika eMiniMalls after the 1st [...]

At the current time, expect stats to be updated around 3:30 Eastern Standard Time at the latest.
The earliest reported update was 1:30 EST, the latest 3:45 EST.

Since Chitika has only been around for a few months, not many payment cycles have been completed.
From intial reaction though, most people found that they were audited very little. With forum owners being audited the most.
It ranged between 0%-10%.
There also needs to be more clarification on Chitika’s part about what they consider a repeated click. [...]

At the end of the month your clicks will be audited.
Repeated clicks from the same IP are removed, as well as clicks from countries such as [b]China[/b], [b]India[/b], and other [/b]lesser developed countries[/b]
Gathered data estimates that you’ll lose about %0-%10 from audits.
Another issue raised is what Chitika means by repeated clicks from the same IP. [...]