If the battlefield is Rockfall Path, can you gank that battlefield?

Yes, you can Gank into Rockfall Path.

According to Rule 810.1.b, Ganking allows a unit to move to a battlefield from another battlefield via a Standard Move. Because Ganking modifies the allowed destinations for a Standard Move (Rule 144.4.c.1), it is a form of movement and not "playing a unit."

Rockfall Path's ability states: "Units can't be played here." Since moving a unit via Ganking is a standard move and not the act of playing a card, it does not violate this restriction.