Do the dragons on Dragon Booster hoard this like dragons in myths do?
Like shiny stuff and the like?

We've never seen a dragon with any possessions at all, so I'd say no. Maybe the orange dragons consider their riders to be their possessions, but hoarding and material objects seem to be of no interest to dragons.

Dragons as they are might not even have any concept of ownership. I've yet to see any instance of a dragon acting as though it owned something.