it really depends on your difficulty level...
If you are playing on Hard, then i don't suggest your survivor becoming summoner, because the creatures you summonned are far too easy to be killed in seconds... and maybe you'll busy casting Restoration on your creature rather than shooting arrows on your enemies. UNLESS you 'happen' to purchase some summoning skill spellbooks or have some itmes with bonus to summoning skills, that will be different.
I'm using a Lv25 warrior and i 'happen' to buy 3 Resurrect spellbooks from the merchant (I got 2 from the mage and 1 from Blake- I almost patronize them everyday!) --> So, i can use Lv5 resurrect. Right now I have 2 Elite Orc Chiefs and the Engineer from the cursed abbey fighting by my side! They all have an average of 2500+ hitpoints and are hard to die. I realise that this can be more useful than summoning which i intended to do so at the start.
Alas, the downside of resurrection is that Your character won't be able to sleep at all!
P/s: the Engineer won't die when you sleep and it doesn't count as one summoned creature (right now i only have Lv2 aura of command)