Those are called Summonings and at the moment it is undecided whether they will exist in the SLO verse. There're pros and cons to implementing them.

What are the pros and cons?

Here: http://www.shinobilifeonline.com/index.php/topic,500.msg4896.html#msg4896

And imo, genjutsu shouldn't do damage. It should be used for things like paralysis, screwing movement (like pressing right and go left) etc.

Genjutsu is such a vague term. But IMO it's just an attack-category, just like Taijutsu and Ninjutsu.
Every attack-category has: Crowd control (soft and hard), Damage (Area of effect and single target), Utility (Heals and Buffs) (Plus Passives).
In that  sense, I presume that genjutsu could be everything from making the victim imagine getting stabbed (damage), to being stuck in a loop (hard cc, fixed timer, interupted by cc). And/or a mixture of the two. Tsukyomi could be both damage and stun. Aka a CC-DoT: Crowd Control + Damage over Time -> These are the once I would expect to be most of.

Not all genjutsu should be breakable. But those who are should be interupted depending on the categorization: Stun: Chakra-release, Immobilize: Self-inflict pain etc... IMO it should also break if you kill or (in some cases) damage the caster significantly. Breakable genjutsus should be the ones with long-lasting effects if nothing is done. E.g CC-DoTs or long-lasting hard-cc that break on damage.

Speaking of cc, it would nice to see some effects have a more interactive taste to them. E.g for blinds or jutsu that impairs vision darkening the user on the screen (as opposed to, as in most mmos, just represented with icons and uselessness for some abilities.)

On the topic of how limited the creator of the (game) universe might be. According to ancient scripture: Omniscent, omnipresent, omnipotent?

In most mmorpg's the game administrators have super-powers. Hopefully he will settle for a super-outfit as to make it a somewhat fair fight.