Optoisolated MOSFET to control a load - should I take in consideration MOSFET typical use?
It defeats the purpose of using an opto if you connect them. The opto's NMOSFET gate-source is floating and the photo emitter that drives it "floats" with it so you can place the load on either side of the source or drain. It works on the high-side just fine.

The reason you normally place loads on the drain of an NMOS is just so you can connect the source pin to ground which makes it easy to drive the MOSFET to drive from a ground referenced signal. The opto doesn't have or need this. It's one of the two main reasons it exists (the other is galvanic isolation).

I think there still is a body diode in that MOSFET so it cannot block current in the reverse direction.