Do they get a range bonus? They still have forward guns, right?

Yes and yes.

Auxiliary arcs are just like normal firing arcs although there may be restrictions on what weapons can use them and maybe when.

Auxiliary Firing Arc

Some ships have an auxiliary firing arc identified by dotted lines printed on its ship token. These ships also have a unique primary weapon icon printed on their Ship cards. When attacking with its primary weapon, a ship with this icon may attack an enemy ship that is at Range 1-3 and inside its primary or auxiliary firing arc.

• When attacking with a secondary weapon, the ship must still target an enemy ship inside its primary firing arc (unless otherwise specified, e.g. on an Upgrade card or Pilot Ability).
• When an effect specifically mentions an auxiliary firing arc, other firing arcs cannot be substituted. For example, Tail Gunner cannot be used with a Ghost or Shadow Caster.

Essentially, mobile arcs and auxiliary arcs are an extra bit of firing arc for the primary weapons only (so range 1 and range 3 bonuses as normal) unless a secondary weapon or upgrade specifically says so.

They count as being 'in your firing arc' for stuff that says so (like outmanuver or autothrusters).

3 minutes ago, Magnus Grendel said:

unless a secondary weapon or upgrade specifically says so.

Just for completeness, a pilot ability can also vary what your auxiliary arcs can be used for, e.g. Moralo Eval's.

Thanks, everyone!