Well, this is what I had in mind:
I imagine FunkySwerve is suggesting something like this:
where "UniqueMonsterTag" is the unique tag in your monster template.
One difference between these examples as they stand is that the first one doesn't spawn more monsters if one is killed, whereas the second one does (unless your monsters leave lootable corpses, in which case the outcome is less certain). A second difference is that if there were two bosses, the first example allows them to summon 5 helpers each, whereas the second restricts it to 5 per area.
Incidentally, the second parameter to CreateObject has to be the template, not the tag, so I wonder whether "tag_monster07" is correct. If the tag in the template is not unique, you can specify a unique one as the fifth argument to CreateObject.
Also, it's perfectly acceptable to use a constant like OBJECT_TYPE_CREATURE in line; the variable nCreatureDes is unnecessary.
Likewise, the variable bAnima doesn't make the code more legible; some scripters put the literal TRUE in line, others define a constant with a meaningful name, such as USE_APPEAR_ANIMATION.