My son had a hernia as well as a baby, luckily it closed on its own, but I recall the doctor telling me that excessive crying does aggrevate the hernia. I am not a fan of letting them cry it out as it just seems wrong to me deep down and as the other mom mentioned you have to trust your instincts.
My suggestion would be to try setting a bed time routine- bathtime (lavender to calm), storytime, you can play soothing music in his room (meditation cds, etc), and offer to lay down with him until he falls "asleep".
Also make sure to cut any sweets and artificial foods out of his diet (ie candy, chips, fast food, juices that are not 100% juice- read the label) These foods effect some children more than others and can get the kids so wired up metabolically that their body can not slow down to rest, no matter how tired they are.
I would not suggest to start rocking him again as it did not sound like it was working anyway as you had to do it for hours and you do not want to go down that path again!
Good luck its sounds pretty frustrating!
A.