Branching from a branch

Hi all:

I've been searching high and low but have not found anything on the  
web similar to my situation.

I've got a project whereby we have to integrate into some source code  
owned by another organization.  That organization uses a CVS  
repository.  With each production release, they create a branch.   
Presumably at some point they merge that branch into HEAD (though I  
don't see any tags indicating that).

My question is, if I create a branch off their last production release  
branch, is it possible to merge my branch back to HEAD in the future?   
If so, should I anticipate any additional challenges as a result of  
branching off a branch?

Thanks for any input,

Wade