Hi,
You are correct in that static UProperties are not supported.
Your other problem is a general C++ issue, where static members are only a declaration, but you haven’t defined it outside the class:
http://www.parashift.com/c++-faq/link-errs-static-data-mems.html
In your case, you’ll need this in your Turret.cpp file:
TArray<AActor*> ATurret::EnemyList;
Steve