DE has Agressive which is the same +1 modifier as Orks and Chaos. The subsequent round thing was pointless, and boarding actions don't continue anymore.
DE have the option to purchase both Incubi Bodyguard, and Wych Cults, which give them Frenzied, and Elite Cadre respectively. So they shouldn't have any issue with boarding.
The Impalers will likely have their resilient save go to 3+ to keep up with fighters.