Loan players being able to play in the cup has been a bugbear of mine for years. Back in 2003, Watford had borrowed Chopra from Newcastle and he played against us in the semi final. Back then, you couldn't loan from another Prem side so we couldn't have loaned him in even if we'd wanted to.
I'm fine with the Cup tied rule and also think all loan players shouldn't be allowed to play cup games either.