Does an ETA cancel a current visa?
Many Australian visas will, after being granted, override a previous visa.
However this does not appear to apply to a subsequent grant of an ETA, as this is different to most visas and does not replace a currently held substantive visa.
A VEVO check after an ETA grant will show the previous visa still active.
Visa Subclass 601, Electronic Travel Authority.
Visa Listing: Subclass 601 ETA