It's impossible to tell what your husband's condition is without seeing the lesions. Best bet is to get to a dentist to have an examination and diagnosis.
Not sure what you mean by "under his gums", but regardless it would be impossible to tell you what it may be without seeing him. It would also be improper to suggest any way to treat it. My best advice is to have him see a general dentist for a set of films and an examination, and if the nature of his "white pimples" is still unclear, I'd see a periodontist or an oral surgeon for a definitive answer.
sorry, i re-read your post....misred "upper" as "under". my response is still the same-- he needs to have it looked at in order to receive a diagnosis/treatment