SOIC-8-EP instead of SOIC-8 is that okey?
If you mount a regular SOIC-8 part on a SOIC-8 footprint with a copper pad intended to connect to the thermal pad of a SOIC-8-EP, it won't cause electrical problems.

But it won't improve the thermal performance much either, because the thermal resistance of the plastic of the chip package is much higher than the thermal resistance of the copper in the lead frame. 

Most of the heat will still have to be removed through the copper lead frame, not the plastic body.

It would be better to use the copper area to connect to the drain pins, as shown in note 1 on page 3 in the datasheet: