1.- QlikView Publisher
A) Publisher is the commercial name for a series of components that facilitate and optimized the way QlikView reloads QVW files with its own engine (using the QDS and QVB processes mainly). Plus, it allows having the two folder structure for Source documents and Distributed (User) documents.
B) In regards to PDF Distributor the answer is yes, if they don't have PDF Distributor, they should be looking NPrinting.
2.- Only QVS users: depends very much on their needs. Personally, I cannot think of any QlikView Server deployment without QlikView Publisher if the number of users is more than a few dozens and it implies daily reloads. If they are big enough or their requirements involve Microsoft Office integration and PDF distribution, they will need NPrinting in addition to Publisher.
Anyway, since you are a Partner, engage with your closer Qlik Partner Manager so he can tailor the proposal to your customer actual needs.