Yes you are correct, Losi is a 0mm offset which means the back face of the 12mm hex is perfectly centered in the wheel.
I believe the 4WD Slash offset is something around +10mm or +12mm offset which makes the wheels extend farther away from the chassis. While this will technically work, you may need to mount your body higher than normal to properly clear the fenders of the body and/or trim the body more than was designed to handle. Performance will be significantly effected by reducing turn radius and more sluggish steering response.
I would consider ordering the proper wheel size and using acetone to remove your old tires from the Slash wheels.
Just use a Tupperware container filled with a couple inches of actone on the bottom, then place spare wheels (or any other object) elevate the mounted Slash tires above the solution.... you want the actone fumes to dissolve the glue without the liquid actually touching the tires. Acetone tends to shrink cheaper brands of rubber. It may take 2-3 days for all the glue to dissovle, then simply pull off the old tires and re-mount them on the new SCTE wheels
Over time, when you wear the tires past serviceable life, simply cut the treads off (at the sidewall of the rubber) to save the foam inserts (which can be recycled many times) then soak the beads of the rubber on the wheels completely submerged in acetone for 1-2 days and then the beads will peel off effortlessly. You can recycle wheels indefinitely.
When buying new tires, there are some brands which sell the tires without foam inserts to help reduce costs
A gallon of acetone typically lasts me a couple of years.... you can keep the acetone in the same Tupperware container and re-use it until there is so much glue that it starts to leave too much gunk on the wheels. You can also use a coffee filter to strain the dissolved glue too.
