You cannot resurrect summons by their CHARACTER_xyz name, because such name does not exist at compile time, that is true.
However consider the following code:
IF
CharacterDied(_Summon)
THEN
CharacterResurrect(_Summon)
This will resurrect summons too.
So I just tried this piece of code:
IF
CharacterDied(_Char)
THEN
CharacterResurrect(_Char);
And got this result:
Roderick resurrected immediately after being killed, but neither of the two spiders summoned were resurrected even after their timer ran out.
I tested whether them dying mid-summon changed anything, and they still remained dead. For whatever reason, summons cannot be resurrected. Is there any proof to the contrary?
Edit:
Actually, I think it might just be that summons never trigger the CharacterDied event. In the combat log you can see that Roderick gets a line saying he turns into dust when he dies (most characters get some sort of line upon death). The summons, however, get no such combat line upon death even if they are killed mid-summon.