Definitely - because I know from experience how painful it is to have those probes under the gumline. No way would I want anyone doing that to my dog without giving pain relief.

There's obviously training and training!  I did it for over 20 years with no problems and certainly no pain relief. :)

I would be most upset if a groomer emptied my dog's anal glands when they didn't need it 

i dont think you can empty 'empty' glands. if you squeeze and they are empty, nothing will come out but it shouldnt cause a problem, they are meant to empty when the dog empties its bowels