I don't really know.
Your use of Citrix is not really important in this question, the
same question could be asked if you had one generic user account
for multiple users, like a lot of schools have in a classroom
setup, or libraries with public-access computers.
What complicates the story is this:
Per User TS CALs were build-in to the OS in a very late stage.
The 2003 TS Licensing server cannot handle them correctly, so
currently Per User CALs are unmanaged.
This means that when a TS server is set to accept User CALs it
will look to the license server to make sure that one is available
but it will not be decremented from the database.
It is your responsibility to have a valid User CAL for every user
that uses the terminal server.
I have no idea *how* the LS will differentiate between users, when
this functionality is build into the next release (SP?) of the TS
Licensing service.
It sounds as if your setup might violate the EULA, but I'm unsure.