I don't actually like the implementation at all, really. In order to implement, you copy and paste this as many times as you have summoning skills you need to limit. That isn't even considering that there may be more code associated with the nature of the summon to begin with.
I think being able to register a spell raw id to the system that is then monitored would be substantially more useful and more modular. call RegisterSummonedUnitLimit(SUMMON_ID, SUMMON_SPELL_ID, KillEffect, KillEffectPath, SummonLimit). The only disadvantage to this that I can see is the inability to have the SummonLimit depend upon skill level. I think function interfaces might be able to solve that issue, though, if I got anything out of Vex's tutorial. :)
If you keep it like this, though, I think the only section of the resource database it would make sense is "Samples."