Abilities » Omega Barrage
If I attack using a Pokemon that has the "Omega Barrage" Ancient Trait, can I do things like attach an Energy or play a Trainer between attacks?
No, you would resolve all effects from the first attack and then either perform your second attack or pass. You don't get to go back into the main part of your turn again.
Source: Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)
Abilities » Omega Barrage
If I only have one energy card attached to Excadrill, can I use its "Omega Barrage" to attack with "Dredge" first to attach two energy cards, then attack a second time with "Mach Claw"?
Yes, that would work.
Source: Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)
Abilities » Omega Barrage
What happens for Omega Barrage if the Pokemon is Confused?
You need to flip for Confusion twice if you choose to attack twice. One flip for the first attack, then flip again if you decide to attack again.
Source: TPCi Rules Team (2015-02-05)