Adam,
I have seen lots of spots/lumps/bumps on snakes of all types and they have ranged from malignant cancers, to fatty tumors, (yes an abnormal fat deposit is still considered a tumor) to fluid filled cysts, to viral pustules, to localized infections...you get my point.
Asking people on here for health advise is asking for trouble.
You did the right thing by going to the vet. She should be able to tell you with some confidence if all she saw was fat cells. It would look like a droplet of oil smeared across her microscope view. Ask her specifically if she saw any white blood cells at all and ask if she feels confident with the answer she is giving you. A lot of times a vet won't get a great sample if the tumor is solid but since she just charged you for looking under the microscope she might be reluctant to tell you that. Often the only way to know is to remove one of the masses and send it to a lab, obviously thats more expensive than just poking it with a needle.
A few questions...
Are the scales over the lumps normal appearing?
Are the lumps movable IE are they within the skin or are they attached to deeper tissue?
Have more appeared over time or did they all appear at once?
The best advice I can give is to measure them all carefully and write down how many and their locations. Or photograph them accurately. If they change size/shape or multiply its time to get one removed and send it to a lab to find out what it really is.
I had a dumerils boa years ago that would get these fluid filled pustules. I did everything under the sun and we were never able to figure out what caused them. Sometimes its just a mystery. I have also seen these fatty tumors that other posters have mentions. As far as what causes those... take your pick, no one understands all the reasons for cancer...genetics, environment, old age, fatty diets, poor temps...who knows.
Good luck and let us know what happens. I would love to see some closeup pics if you can.
Cheers