It's a running gag that Kellam isn't noticeable to his comrades... but to have it happened in RL too is just ROFL. XDD
Well, Kellam is basically the only armored unit you'll get (besides Kjelle, but there's a are certain requirement in getting her), so it depends if you'd like to use him or not. You can still complete the game without him, he doesn't really hold any significance in-game, but it'd sucked if you aim to collect every single character and their endings only to miss him out.