Town owners, subowners, and Lords (level 4 members if you have unlocked them at Town Level 20) can all setup and deploy Inhibitors and Town Generators.
As for Beacons, you cannot 'click the button' to turn them on (only town members can do that). However, beacons do not discriminate between who they teleport once they go off (Knife travel is not so controlled). As beacons state, all players within 8 blocks of them will be teleported to their selected destination after 15 seconds of hitting the button. This means friends, foes, and mercenaries alike (regardless of being a member of that town) will be teleported. This all works in reverse with Inhibitors as well.
So as a Nomad/Wanderer you cannot build Inhibitors, but you can certainly participate in a fight. You will however suffer from any disadvantages such as not being able to use the town portal of whomever town you're fighting for to get back if you die, of course. You'll have to hope your home is near enough to the town or the attacking destination.
But if you're in said town at the time and choose to travel via their beacon if they let you, you certainly can.