First of all, I don't think there's really any (non-joke) build that's UNviable in the sense that you wouldn't be able to beat the game with it.
But anyway... Charmer/Summoner is an OK combo. Obviously, presence works well for both.
However, some of the best leaderships items right now (important for buffing your summons) such as Helm of Heroes and Conqueror's Breastplate encourage tank builds rather than tease-builds, and there's really no reason to go Charmer if you aren't doing a tease build to take advantage of Stylish (assuming you aren't against multiclassing).
But anyway... Charmer/Summoner is an OK combo. Obviously, presence works well for both.
However, some of the best leaderships items right now (important for buffing your summons) such as Helm of Heroes and Conqueror's Breastplate encourage tank builds rather than tease-builds, and there's really no reason to go Charmer if you aren't doing a tease build to take advantage of Stylish (assuming you aren't against multiclassing).
Running several charmer skills while being a summoner? absolutely viable. But generally you want to spec into support and tanking if you're going to focus on high leadership and summoning allies, to buff up those allies. Things like Bless, and skills that draw aggro, so your allies can do the most work possible.