In most cases, "dude" for a man is not a very respectful address. Only if you're very familiar with a person,and he knows it isn't meant as a disrepectful address, but rather as a sign of a very close friendship, you might call him "Dude". Adolescent boys aften call their pals this way.
Synonyms might be "pal" oder "buddy".
But, conversely, if you're addressed by a stranger by "Hi, dude!", it crosses a line and is considered very disrespectful. Only, when it comes from a person from the same age cohort, it can be accepted, when it's obvious it is meant in a cordial way.
"Dudette" is the female form of "dude", but it's not really used, as far as I know. GymGlish uses the female form as well because the GymGlish robot doesn't really know wheter the participant is male or female. Hence, it calls you "Dude or Dudette" to cover both genders. When GymGlish calls you "dude" oder "dudette" , it's meant in a friendly way, of course.
I don't think dude is that disrespectful! It is in the same way that overfamiliarity is in general - but it's not a disrespectful word in itself, as far as I'm concerned. Still, thanks for your answer!