1. I think I land it just about every single time I try in field PVP, though in arena PVP it seems to be about 1/3 chance.
2. Ask the summoner. Dark Avenger has a panther, which is fighter type. I think... big boom, unicorn merrow, and... I know there's a third that can use mage buffs.
1. Pretty high, not 100% but certainly higher then 60-70%
2. Depends of the summon, but asking the summoner is always best. With a PS it is Nightshade, Soulless fighter buffs, Warlock Kai is fighter, Queen has enough on pure defensive buffs. Never had to buff an ES so there I don't really know.
Practically you want to give most summons in group fighter buffs, unless they are pure support like Queen.
We've found that Big Boom + Empower + Acumen is a great way to add that extra little oomph in your AOE groups. I didn't think it matters, but our Warsmith swears up and down by it.
Most summons receive fighter and mage buffs. The exceptions are as follows, if it's an SE buffing.
Fighter only
PS: Shadow
Warlock: Kai the Cat, Kat the Cat
Elemental Summoner: Unicorn Boxer
Dark Avenger: Dark Panther
Necromancer: Skeleton, Cursed Man
Warsmith: Mechanic Golem
I'm not sure (never bothered testing) whether the Cures for Unicorn Seraphim and Queen of Cats are based off MAtk.
Give Necromancer's zombie (that green man ... how is it called ... Corrupted man) also Empower and maybe wild magic. Fully buffed 70+ corrupted man can have 1800 matk which is NOT that little (my BF's 65 SH had less than that thing). But not many necros use it's magic power, mostly it's only TP tool for them.