Is casting symbol of pain truly an evil act? Only if one's soul hasn't been purified by the burning flames!
When one is summoning or even calling known evil creatures that are beneath their humanity, it is proper that they should serve their betters, those that are of the burning flames.
“Take him, my slaves! Drag his soul back to your dark masters!” —Argyll Te’Shea, servant of Pelor and malconvoker
It is indeed good to use the lesser races (even allies) as stepping stones to achieve one's own worthy goals.
If one aspires to reach a level of burning hatred for the undead that is close to his master's, even one with such devoutness as a Paladin, he must be taught (in a round about way) to strive for even greater vengeance!