Well i think the major problem with mobs that can summon you more or less can use em to solo pull stuff.
So no risk to get adds during a pull where you would have 3 or mobs aggro once u pull one.
Also on the note of charmed pets but not summoning but ...
Mobs sometimes assist the Charmed pet ......
Happend once so far in Kael send charmed Giant against another Giant and a Giant close by attacked the mob the charmed giant attacked.
In seb as i had Echo of Sebilis DC ( which i think should recieve a uncharmable tag) went to disco and out of sudden some jin frogs where assisting echo against a krup or illis frog.