It would be, but it has a slightly different meaning though. The example above can be also said when referring an orgnization, or a formal group, or like a school club. But yours can be used when for example there is a project being done by students, so everyone will do it. You can ask like this someone that you already know he or she is doing the project but emphasis is on whether they are making it individually or with a group, by this way you can ask to be together for example.
bir sorum var,
bu beni grubun üyesi diyor mu? yoksa
"Neredesin?" "ben dükkanda dişında bir grubun içindeyim"?
If I completely messed up the Turkish, I asked if this meant if I was a member of a group, or would it literally mean I am within a group of people outside a store (if somewhere asked where I was.)
I believe most specific groups (including a dance group) will be noun compounds, so the "group" will have a possessive suffix: dans grubu. In these cases, your sentence structure is correct: Sen bir dans grubun incinde misin?
If you are describing a group with an adjective, just remember the "bir" goes between the adjective and the noun: Sen büyük bir grubun incinde misin?