Can I play Rengar Trophyhunter to Rockfall Path?

No, you cannot play Rengar, Trophy Hunter to Rockfall Path.

Rockfall Path has the static ability "Units can't be played here." Per Rule 054 ("Can't beats Can"), a card that forbids an action supersedes a card that permits that same action. Rengar's special Ambush permission lets him enter battlefields where enemy units are present, but it cannot override a hard "can't" restriction from the battlefield itself. Rockfall Path blocks all units from being played there, regardless of keywords or special permissions.