You only need one dual player enabled and one normal light gun.
No, not if you only want them used for mame (or use win2000). Two normal lightguns work great in current official mame.
The dual player model is only needed for
non-mame games (aka non-rawInput games), or mame prior to the switch, or win2000 computers.
The only things you need to do to use two normal guns in mame is to leave "-dual_lightguns"
disabled and remap as needed. Oh, and use the standard mouse drivers, no fancy "dual mouse" drivers.
OTOH, if you want to play other games that are compatable with actlabs dual player gun, go ahead and buy one of each.