Jameson didn't want to hire Smythe originally. He was convinced into doing it by another Bugle employee...Peter Parker. Peter needed cash because it was a lean week for villains so he convinced Jameson to hire Smythe's robots thinking it was a jobber he could take out and score some easy cash, he even convinced Jameson to pilot the Spider-Slayer robot.
The Spider-Slayers is Peter's fault more than Jameson.