Is "camp" short for "campaign"?

It isn't short for "campaign", and "camp" should probably be omitted from the sentence.

Checking stackoverflow.com, I find four uses of "open source camp":

• "Crippling software is not favoured by all (especially the open-source camp), ..."

• "... if you lean towards the open source camp, I suggest you use MySQL ..."

• "I'm also looking for something in the open source camp (such as rdesktop) ..."

• "I am a developer in Peking,China! My major occupation is software engineering with microsoft dotNet framework. And I am very intrested in open source camp."

The first three (from a question, an answer and a comment) are the normal usage, note they're all "the open source camp". The meaning is as others have answered, a shared belief system, supporters and defenders of open source.

The fourth one is from a user's profile, and must be the source for this question. In this context, the use of "camp" is unusual, possibly incorrect. First, there are some typos and English probably isn't the author's first language. Second, it would be better to include "the". Finally, you wouldn't normally say you're interested in "the open source camp"; when talking of "the open source camp" you'd usually be talking about the beliefs or opinions of the wider open source community.

It would be better written something along the lines of:

• "And I am very interested in open source."
• "And I am very interested in open source development."
• "And I am very interested in the open source community."
• "And I am very interested in the open source ideology."

It's worth mentioning in passing "camp" is also often used in software circles for unconferences and hack-days, such as Foo Camp, BarCamp, CloudCamp and RecentChangesCamp.

Camp here may refer to a group sharing an opinion. He might be describing himself as a supporter of open source software.