Hi Galin,
Sure, it is possible, there are several ways for it.
It depends what are you using ISIM for.
First of all, let us agree on terminology:
We (people using ISIM) tend to call "users" the users registered in ISIM, either through some HR feed or manually.
Then, these users may get accounts, on different services, like AD, or even ISIM itself.
So, what you need to have first, is an user in ISIM (you can't create AD account to nobody, you need owner first). Then you go (in manual provisioning) find that user, and "request account" for it. Find AD service, and here you are in form for account add request, where you may want to set some of AD attributes fields, including group membership (search box).
At the end, you submit request.
This is the simplest example - we usually do not do it this way but rather over policies or accesses, but functionality wise thit is it.
Hope it helps,
Mita