Do the wheels on my dock have to face out?  

You can install the legs with wheels pointing in the direction that makes the most sense for your layout.  For example, getting your boat lift closer to the dock may mean turning dock wheels inward so they don't interfere.  Loosen the bolts and nuts on the brackets that hold leg in place.  Slide the leg out and turn it to the desired position and slide it back in.  Re-tighten bolts.