Some time ago my company got similar challenge when needed to scan in remote desktop environment.
We tried USB redirection solutions but there was problems, especially that redirected scanners (USB devices) can be accessed by any user logged to remote session.
Also, I notes that there are special scanner redirection solutions on the market that works in other way. I spent several days tried different solutions and for my company we decided to use Scanner for Remote Desktop.
It redirects both TWAIN and WIA interfaces
It isolates scanners in multi-user environment
It works in RDP and Citrix
It works fine with scanners that we use.
I hope this will help you.