It is very common for belly dancers to be afraid of performing in front of other belly dancers. I used to feel like that too and I still do every now and then but that fear has eased substantially over the years.
One of the biggest fears is that other belly dancers will figure out where you went wrong in your choreography. Really, we don't know. There is no way for us to know where you went wrong in your choreography unless you give it away. So if you have a good poker face, we won't ever know. Heck, there have been a few times when one of my students added in her performance one of our ITS combos but the combo had been tweaked... or so I thought... so I would say something like "I really liked what you did in that combo, how you modified it." and nearly every time, the answer was "OMG! I messed up the combo! I had meant to do it as is." And that is when I teach them the lesson of just saying "Thank you!" :p So, again, I knew what the combo was supposed to be but they had changed it... and I had no way of knowing that it was an accident. ;) There actually is no magic guide that tells me where you went wrong unless you tell me either through your words afterwards or in your face during the performance.
Another fear is that dancers will see all your technical flaws. Well, yes, it's possible that we'll see them. Generally, though, that thought will quickly come and go, especially if you're really flowing with the piece.
You may also fear that another dancer would disagree with how you choreographed the piece. Well, you know, there are many ways to skin a cat. So while, yes, I may have had a different approach, yours is valid too.
Really, what it boils down to is the fear of being judged. Unless you're participating in a belly dance contest, you won't be. Seriously.
On the surface, dancing for the general public seems like it's so much easier. And it is easy. But, actually, there are a number of advantages to performing in front of a belly dance audience.
You'll have the benefit of an educated audience. They will know what belly dance is (and isn't) so you don't have to educate them as to that. For example, you won't get the "take it off!" cat calls. But more than the crude comments, they'll actually understand when you're doing a piece that is more folkloric or the intricacies of lead/follow in ATS/ITS or things like that.
They'll also be technically savvy so your amazing combo won't be lost on them. The general public will have about the same reaction for a simple hip drop vs. an amazingly well layered combo... seriously, they won't see much difference. But the belly dance audience will see the difference. They will also realize when a simple isolation has been very well executed.
You can get valuable feedback if you ask the appropriate people (see this previous blog entry on that topic: http://celestesmusings.blogspot.com/2010/09/finally-long-awaited-follow-up-blog-on.html ). I know, you don't want to be judged and all but you can ask someone what they thought about your performance, what can be improved upon, etc. This is material that will help you grow and you simply won't get that from the general audience.
Understanding of your level
For the general public, they won't realize the difference between a belly dancer who has been doing it for 6 months vs. 6 years... so they will lump all performers in the same bucket and judge you equally. So, yes, of course, your performance may not stack up but they won't get that nor why. A belly dance audience will totally understand what your level is and will assess your performance at that level.
We're all in this together
Another thing is EVERYONE who performs gets nervous before going on stage. Seriously. Even Rachel Brice and Ariellah and Tempest and < insert any dancer's name >. So there's this element of "we're all in this together" that brings us closer and makes for a supportive feeling that you won't get from the general public. In the general public, just a few people are performing... in a belly dance crowd, lots of folks will step on that stage... so they understand what it feels like to step on that stage.
So while, yes, a general public audience is less nerve racking, a belly dance audience is not nearly as much of a monster as you make it out to be. I seriously can count on the hands of one hand the events when the belly dance audience wasn't extremely supportive. And I can't think of a time when it was downright hostile. It's really all in your head.
Having seen also a number of dancers who very rarely perform for a belly dance audience, I can also tell you that I've generally seen less improvement in their performance quality than those who routinely dance for belly dance audiences. Again, I strongly believe that you will learn a whole lot about performing by dancing in front of other belly dancers. And they won't judge you the way you think they will.