Pigmented skin patches aren’t uncommon in Malamute. These will often be “macules” which are basically just large freckles. The black colour comes from melanin pigment produced by special skin cells called melanocytes. They can occur all over the body but we will often notice them more on the underside 9if that’s where they are) because of the lack of coat cover. If that is the case there will be nothing to worry about.
However I have some concerns with what you’ve described in that these lesions are raised and perhaps a little scabby. Melanomas are reasonably common in dogs. These are skin cancers and some can be malignant. As a very rough rule, the further away from a dog’s mouth the melanoma is, the less likely it is to be malignant but we cannot rule that out completely on the abdomen. I would strongly recommend that you have these spots assessed by your vet. If they are melanomas they would need to be excised surgically. The underside is a convenient place for that to be done as the loose skin allows for a wide excision. However the risks of spreading are much less the sooner a melanoma is removed.
I hope I’ve been of help.
Kindest regards, Peter