I understand your point, but what it entails is using a floating point number for the aliens' frags. I don't like this for a couple of reasons. Firstly you will get the situation where you score damage from a kill but your frag counter will not increment, even though you
have gained a (partial) kill. Secondly it's basically the same as what the humans do. I like the fact that the teams in Trem are really very different, whilst the game is (almost

) balanced.
Besides these though, doing this doesn't actually change how frags are distributed in relation to damage. After a number of player deaths it averages out quite quickly. For example, three aliens killing the same human collaboratively three times. (This is idealised for the sake of argument). With an integral approach each client gets a frag each. With a floating point approach each client gets a third of a frag each three times... it ends up the same.
Of course I might be misunderstanding -- maybe you want lower classes to actively be awarded more frags, so it's easier to become a higher class than it is to maintain being a high class?