Adam Mitchell played the first half for Red Star in a 9-2 friendly Charity match win in Kosovo against Gračanica (a Serb enclave). By all accounts he's performing well. No news on whether he'll be offered a contract yet though.
If you want you can watch the whole match here.
Also, here's an eye-opening article on the same fixture last year.
As an aside, Kosovo was voted in as a member of FIFA earlier this month, as was Gibraltar.