At a time when Spidey was an outlaw who was wanted by the authorities, if you want to split hairs. And it was the Jackal's first appearance, so Punisher didn't know his true agenda.Whatever label you want to put on the Punisher, he first appeared in the pages of The Amazing Spider-Man, working with Spidey's foe the Jackal--He's part of the superhero genre.
Err, yeah, the villain part of the genre. Like you said, he worked with Spidey's foe.
Doesn't matter anyway...whichever side they're on or methods they use, they're all part of the same genre.
Plus he teams up with Spidey in the 70s as well then they retcon his first appearance as being (unwillingly) under the influence of drugs.