I haven't tried it myself but I think it would be possible to run Tomcat on one machine, IPS on a second and then the Job Server on a third. I think you would be absolutely nuts to go to that length. The install would suck and the maintenance and upgrades would be even worse.
Sometimes, the customer isn't always right. If one of my clients wanted that I then would ensure that they were willing to pay me a bunch of money and that I didn't have to support it. But I would be emphatic that it was not a good idea at all.