can a top/bottom feed style sub-panel be fed from back of panel
The panel has knockouts all over the place.  They don't care which knockout you use.  

"Top or bottom feed" doesn't pertain to where on the panel the EMT enters; it pertains to where on the busbars you attach the wires.  

The very fact that you have a choice of two sets of lugs (top and bottom), implies this is a main-lug panel (not main-breaker) and it either has


symmetrical screws (so the whole busbar assembly can be unbolted and installed upside-down) or 
has "thru lugs" (a second set of lugs on the bottom of the buses) is intended for if you want to continue power to a second subpanel.