We know who they were, but the movie never showed us why Tomar-Re and Kilowog would break ranks and chase after Hal, because Hal never spent enough time around either character to really establish any sort of friendship.
In my mind, it wouldn't be so much an issue of friendship; it would be a statement of integrity as Tomar and Kilowog feel that abandoning anyone to their death is not the Corps they signed up for. Whether it be a person, a planet or a galaxy, the Lanterns keep fighting to the end. Up until that point, the civilizations that had died were because the Lanterns either couldn't get there in time or couldn't stop it despite attempting to; it wasn't until Earth that the Lanterns were being asked to just stand by and watch the planet die as an acceptable loss.
That's what we're missing with the scene I talked about. Without that scene, we're just jumping to "Oh, these were the other characters that talked to Hal, so that must it." I think the characters would have acted the same way even if it was someone else; I think it was a defining moment in the characters of Tomar, Kilowog and Sinestro. It laid the groundwork of why Tomar, Kilowog and Hal could be good friends; they all thought the same way.
Again, that's all speculation. Instead of the above, we got cardboard cut-outs that showed up to rescue Hal apparently just because they happened to talk to him earlier in the movie.