I am playing summoning+warfare+poly just fine, it works great, because summoning is amazingly versatile as it doesnt depend on any stat.
@MangoMan
Dont give points into CON... ever
And just take your main attribute which you want to use to deal damage+memory for skills you want and lot of wits so you go first with your summoner
My MC also is a melee Summoner/Poly/Warcraft hybrid and the build works great. I can confirm CON is a wasted stat, but I would recommend taking the Picture of Health talent if you want some to put some more meat on your bones (Each point of Warcraft adds 3% Vitality, almost doubling the 3% or 4% VIT bonus for each level attained). If you're still not convinced, take Five Star Diner as well (Food and Potion effects are doubled).
I play a Lone Wolf tandem (my teammate is Sebille whom I've specced as a Scoundrel/Poly/Warcraft hybrid) and for my MC I put nearly everything into Summoner, STR, and WITS with just enough in Memory to maintain the build. Although (as stated earlier) it is a good idea to put one or two points into the elemental skills (GEO/PYRO/HYDRO etc) to help set up Incarnate infusions and Elemental Totems, in my group we just burn down the physical armor and kill with burst damage and blood infusions/totems. There are plenty of other ways to set the elemental stage so to speak (grenades, scrolls, elemental arrows, etc) so you can throttle your Summoner skill to 20 in a hurry if you're creative
