Evil isn't a Christian term, really...
And by that logic, no human terms should be applied to any alien in fiction.
Humans had the concept of evil long before Christianity arose. And Star Trek's "aliens" are obviously just humans in disguise. Maybe "real" aliens would be so unlike us that "good" and "evil" wouldn't apply, but Star Trek has never been like that.
What else would make them evil? How about someone who thinks evil thoughts but never acts on them and for all outward appearances is a saint? Is that person evil instead? I'd call them extra saintly since they are squelching their impulses so thoroughly. All that matters is what someone does, not what they think.But does doing evil deeds make a person evil?
Conditions were still terrible, but I think without Dukat they would have been far worse.
He could have done a lot more to help the Bajoran. He could have sabotaged the Cardassians as much as possible without getting caught; he could have rebelled and helped the Bajorans overtly. They might have killed him as a probable spy, but at least he would have taken the chance. Or he could have gotten away to the Federation and requested help for the Bajorans, or just hid out for the rest of his life. At least he would no longer be part of an evil system.