You can copy code from one virtual user to another, these are just .C programs. This can be a tedious process as data structures with similar names many be used in both the Oracle Forms and the PowerBuilder recorded virtual users -- I am assuming that both of the applications are making use of the same Oracle API (and version) to access the database.
You can also merge two different types of virtual users, for example an ODBC user for PowerBuilder and an Oracle Vuser for the Oracle Forms application. Mercury has a Whitepaper on how to merge two different virtual user types and your rep should be able to provide this information -- The field SE may even have a copy of it at hand. This merging of two different virtual user types in some case may be easier than merging two users of the same API type.
I would consider an on-site eval to answer your questions on how time consuming and difficult would it be to merge your two applications Vusers into one script. Weigh the time cost against the additional cost of the additional virtual user types. If you choose to go with two different virtual users you will also have to implement a handoff mechanism for the second application to complete the process began by the first -- commonly handled as a file written to and then read from. Or, you could simply pre-seed the database with an appropriate number of half-completed transactions prior to your test kicking off.
iTest Solutions, Inc
I just want to add that the Oracle forms Module is not what I would call one of Mercury's most mature modules, We have had a heap of problems, I still beleive LR is the best product for creating forms vusers but be prepared for and don't hesitate to make service requests-- also check MI's discussion forms--for info
Oh the boredom... of endless space---"Pigs in Space"-The Muppets
Oh the boredom... of endless space---Pigs in Space-The Muppets