If I were executing a 51% attack, would I be broadcasting my state of the network to nodes?
Yes, both scenarios are possible.  The validity of a block is determined solely by its contents, not by when it is broadcast or received, so the attacker's longer chain is equally valid whether they broadcast it as they go, or all at once.

(There is an exception to this principle on testnet because of the 20-minute rule, but that's not relevant here.)