Can paid for Linux applications be classed as promoting Linux?
Yes. This is so because (as Joe says) the software makes use of the
Linux kernel. In the same way that software written for a proprietary
(or indeed another open source) operating system promotes the use of
that host OS.
If the question; can paid for Linux applications be classed as
promoting GNU/Linux were posed then the answer might not answered so
straight forward. Mere pedantry? In the context of a LUG discussion? I
do not think so.
My opinion on this is that I think it does promote "Linux" because
many people distrust and do not understand the word free in free
software (There is no distinction drawn between Open Source and Free
Software within this group of people). For some folk there is an
implication of higher quality the more money is required in exchange
for software. If awareness of such software in this group of people is
raised then so will be their regard for Linux.
I also have no problem with running proprietary software designed to
run natively on a distribution of Linux. The Crossover software from
Codeweavers (and their contribution to Wine) is a fine example. If you
are pro Free Software then you are pro free choice. You can't in my
view criticise the choices people make about which software they run
without the risk of accusations of hypocrisy.