The side-on profile (0:00 - 0:05) is very Kogawa-like (he hated the simplistic lip-flaps of TV anime and frequently tried to push for more unique uses of perspective whenever possible) though he didn’t do a lot on L Gaim so I’d assume that particular part is probably Kitazume or some other Bebow person.

I think the Kubooka guess is pretty apt. The episode only had 4 KA like most of these old Sunrise episodes , and if Kitazume did indeed do that rather long mecha battle at the end, then it going: Intro section with Amu and Kyao - Terahigashi, Lillin's assault on the Works - Kubooka, Amu coming and warning them about the next attack - Onishi ,and then Kitazume covering the final section himself, just as we have it, makes sense to me.

I think usually the Bebow people work together on the episodes and the teams are somewhat static, I would have to check again. But I think that Kanayama and Sakamoto generally bring in other people on their episodes and they cover most of the non Bebow episodes, where if it's a Bebow AD it is mostly other Bebow staff with them.