Nope. You can only access the final boss from the hell gate. Specifically, you need to have sex with all 4 of the sex machines in front, and not get carried off the sides of the screen by the floating jellyfish (which does not count as one of the sex machines and dies in one hit, but respawns infinitely after a short period of time). You also need to have recieved enough sex attacks over the course of the game to fill up the bar at the bottom right of the screen so that it shows a key.
This presumes that you were playing through the game normally and reached that point the hard way. You can also cycle up through the cheats back around to the beginning (no cheats) when selecting the level and there will be a 'hit' sound effect and the screen will flash slightly. This gets you to the unlock point so you don't have to repeatedly get caught by the jellyfish and struggle out until you get the key.
Now since I personally never manged to figure out how to do the masturbation moves that heal you, I have to cheat and turn on infinite health to get through the door, because otherwise you just don't have enough health to survive through all 4 machines. If you know how to masturbate and heal, this is unnecessary.
Edit: Also to anyone not aware, the ending you get is deterimined by the amount of sex moves used on you over the course of the game. You need a certain number to open the door, which turns the bar at the bottom yellow and shows a key, but if you take a certain number of sex moves beyond that (unsure of the exact number but it's reasonably high) the bar begins flashing red. Once you beat the final boss (which is nearly impossible due to the fact that it regenerates (I've honestly wondered if it regenerates because I have my own regeneration cheat on and if I wasn't cheating it wouldn't regenerate like that, but I can't test that because I don't know how to heal myself and get through the door without cheating)) then if the bar isn't flashing red you escape with everyone else to a happy ending. If the bar is flashing red then you help everyone else out, but get snagged by a tentacle as you leave and don't make it out before the entrance closes, to a typical bad end of endless sex.