There is not FAR guidance for logging time as an instructor since there is no rating or currency requirement that involves dual given. You can log time as an instructor just as you can log time in Canadian airspace or time de-icing.

The usefulness of time as an instructor is probably greater than time in Canadian airspace or time de-icing, however your ratio of LCA time to total time has more to do with your company's growth than anything you do. That's not to say you shouldn't log instructor time; if two guys from the same company have both been LCA for the same amount of time but one has logged his instructor time and the other didn't I'd say the guy who logged his time has a small advantage if everything else is equal...unless his instruction time was unusually low.

I never logged LCA time but I didn't interview either so take my analysis with a grain of salt.