You can use it (and live with the severe guardrail) as long as you have the UDFs installed on your data base. UDFs are the custom java functions loaded in your data base and most implementations do not allow these to be installed in their DB. So its your call.
Also when you say you cant expose the column- is it a property on top level page (the class u r querying) or property on a nested page or page list?
If it is a page list i recommend to write a Declare Index or if it is on nested page, create a new property on top level page, write a declare expression to fill it so that can be exposed.
Or any specific reason that you cant expose?
If you use an unexposed property on a report def and UDFs are not there , there will be runtime exceptions like cant read from pr_read_stream etc..