I've used a str based summoner in a mage party because I needed a pack mule. Unless you're comfortable with constantly managing your stash I would recommend to have one (plus you need someone to open these sarcophagi). He should also be the luck guy so that he loots everything.
I would advise against going 2h with him since he won't do all that much damage. Instead go sword + shield, ignore warfare except for maybe bouncing shield and get all the support spells like haste, armor spells, etc (try to get elemental skills from gear until you're summoning 10). Put most points into str and con.
For elemental mages you have an option of maxing 1 skill and getting summoning and/or some support skills for times when your damage type does not work or spreading out in 3 or even 4 schools and maxing your damage with crits instead. The latter approach is more viable lategame since you'll likely get a lot of points in all schools just from gear and also you'll finally be able to get a decent crit chance. I would still recommend having teleport and netherswap on everyone.
