Description:

The package hplip is flagged as dependency of cups. But for printing on hp-printers without using cups, cups is not required although hplip is.
Therefore, in my opinion, hplip is not dependency of cups.

I for instance set up an deskjet-5550 printer by hp and printed without spooler by typing:
$ foomatic-rip -P <printer> <file>

It worked only when hplip was installed, independently of cups.

Steps to reproduce:

(You will need a printer supported by hplip to reproduce this!)

Remove cups (if installed):
# pacman -Rn cups

Install hplip without dependencies:
# pacman -Syd hplip

Manually install other dependencies of hplip (foomatic-db-hpijs should do):
# pacman -S foomatic-db-hpijs

Set up your printer without cups as described on
http://www.linuxfoundation.org/en/OpenPrinting/Database/Documentation