Calling application pgms from threaded web services

I have been playing around with Apache and ILEastic to set up a web service
that will call a process in our existing application. I have both of them
working, but have a question on threads.

ILEastic says the RPG programs have to be compiled with
Thread(*Concurrent). I did that with the front end program I created for
the ILEastic server, but do I need to do that with all the programs in the
existing application that could be called by this process also? None of
the existing programs will use the ILEastic procedures at all. I see
ILEastic includes il_exitThreadSerialize and il_enterThreadSerialize
procedures, but I cannot find anything on how or if they should be used.

And I guess I have the same concern on going the Apache route too since
that also uses threads. Is it safe to call existing application programs
from these web service interfaces without having to modify them?

Thanks for your input! This is new territory for us.

Rick