Well, I started to make this a long post, but I'm going to keep it short.
From what Beggar's saying, I suppose my Ilmateri cleric should cry when he sees the poor rats, starving to death in the sewers. Or maybe he should weep for the poor burdened, suffering, and enslaved donkeys that live on the surface. Come on, that's silly. And the animals we're discussing are planar beings, they will have no recollection of suffering, and their "suffering" on the material plane is the best preventative measure for REAL suffering when someone gets a giant spike driven through their leg.
I'm gonna be frank about this one, the notion that the gods give a damn about how you use summoned animals (putting aside their use as a spell, such as using them to injure innocents or whatever) seems absurd. MAYBE Lurue and Eldath would wonder why you didn't just throw a stick or heavy rock at the trap, but there's no way to do that now is there? Hmm... new spell- Summon Stick? Or, perhaps these two deities would be a little disturbed at the grotesque scene caused by the material plane "death" of the summoned creature, but they're far too wise to be disturbed at the fact that, all things considered, NOTHING HAPPENED to the summoned creature.
Rereading my post, it has a sort of hostile tone. I don't suppose it's the tone I meant to have, but other than being an interesting OOC thought I can't see any logical reasons why the gods would care about this, thus making it a moral issue. Even Beggar's humorous post concurs with this- at the end, he points out that everything he described doesn't actually happen. So why would the gods react as if it did?
The only question remaining that might justify this as a cruel act is whether or not PCs know what happens to extraplanar beings after they are summoned and killed. I don't see why they wouldn't know about what happened, since wizards can and do travel to other planes, they see what it's like on the other side, and they potentially come in contact with the gods themselves.
One last thing. The example animals being used are squirrels and unicorns. Nobody springs traps with these kinds of creatures! Everyone uses rats! The only deities who might care about the wretched little rats are Talona, Moander, and maybe Eldath 'cause he's a rediculous deity anyways.