This is a very interesting and important question, which I've worried over since the site began. My vision for the site is that it would be a place where everyone who cares about the Bible has a voice. One of my first meta-questions concerned a question of mine that excluded (at least in theory) any Jewish answers. I issued a challenge to ask more Tanakh questions. If we have one tag to talk about the Hebrew scripture, I would prefer it be called tanakh and not old-testament. I'd like to see our name change to Biblical Studies which explicitly includes scholars from all traditions. These proposals have received wide support from our current set of users.
You express concern with whether Jews should participate on a site like ours. I am also concerned. In fact, I put considerable thought into exactly that question on Mi Yodeya. As far as I can tell, there is no religious reason for Jews to not participate here. Further discussion of that point should be taken up on the site about Jewish teachings.
What I can speak to with authority is the position of the Hebrew scripture in Christianity. It is the promise that we believe is fulfilled in the person of Jesus. I know a lot of people (including Christians!) ignorantly assert that the Old Testament has been replaced by the New. But that's like saying a building replaced its foundation! We no longer have a Temple in which to offer sacrifice, but sacrifice was never an end in itself:
For I desire goodness, not sacrifice;
Obedience to God, rather than burnt offerings.
—Hosea 6:6 (NPJS)
Or to put it another way "sacrifices shmacrifices"!
The fact is, we respect each other's beliefs because they aren't that different than out own. Sure, Christians believe that Jews haven't finished reading the story and Jews believe that Christians jumped the gun on declaring the arrival of the hope of Israel. But when we get together to talk about the Bible, we have a lot to say before we start having serious disagreements.
As for the perception that our site is "Christian", I'm afraid that's a function of demographics. It turns out that new people who find our site are overwhelmingly Christian because the number of Christians is much higher than the number of Jews at the moment. Other people groups would be even better represented if they commonly searched for answers about the Bible on the internet. We are also beginning to address the imbalance.
In the meantime, I'm excited that you, as a Muslim, have decided to participate in our academic quest to understand the foundational documents of Western Civilization. Please recall that our primary goal is to learn from each other. We will not tolerate any attempt to drive a wedge between religious (or irreligious) traditions.