Hello and welcome to HCM,
If this is the first time his salivary glands are infected and the swelling is not much ( i am assuming that your are referring to the submandibular gland
) then you just need to treat the infection and control the blood sugar levels.
If he does get recurrent swelling and infections only then surgery is advised
Also if the doctors have found anything innocuous like a stone then you may consider a minor surgery to remove the same but do think twice before going to a full blown surgery
hope he recovers soon
Dr Sriram Nathan