When you are attempting to close a gate by fighting…can an Ally assist by adding his fight modifiers? Can you use any other additions for the fight …

Eric

When closing a gate (or atempting any other fight check) you may use everything that gives you a +X fight bonus, this includes allies, skills or items. The X value is simply added to your fight value for all purposes.

Note however that closing a gate is not a combat check and you can not use items or allies that gives +X to combat.

Correct me if I'm wrong but I'm quite confident in this.

You're right. Same stipulation for Lore checks vs. Spell checks. Thomas Malone is a decent ally to assist you with closing gates.