The orcs were the ones that opened the door. As far as getting Dorgath in for melee with them, corridors like this are generally too narrow for more than two of the Warriors to be engaging in melee. Typically that's been Throg and Dorgath because of the marching order, but if the Warriors were ambushed from behind, it would be Carrow and Kelgar (until one of them moved to make room for someone else, at least). It's currently Throg and Kelgar simply because Kelgar was closer than Dorgath to the door when it opened. Whether Kelgar would attempt to move away from the orcs to give Dorgath an opening (which he may or may not be able to do when they're charging at him) or hold his ground and attack is sort of a matter of preference. Right now, Kelgar has the lowest Weapon Skill of anyone in the party, so he's the least likely to hit in melee and also more likely to be hit in return. But he can compensate with his hammer, potentially the most damaging weapon anyone has other than Throg's once-per-adventure Mighty Strike (but it's Dorgath whose hits have the highest average damage, thanks to his Great Axe ability) and also with his blessings (he can heal himself, give himself an extra attack, boost his Weapon Skill, or give his attacks an extra chance to hit). Basically, the Warrior Priest is sort of a hybrid character that can either use his powers to aid his companions or to enhance his own melee abilities, depending on the situation... ...but I don't know which Melkor wants here, so I'm sort of leaving Kelgar on autopilot based on how he acted in the previous adventure.