no Im sorry foxholes do not seem to be equivalent to slit trenches, units indide foxholes can be picked off quite easily where slit trenches make the unit inside near invincible! I wish that was the case though.
[...] What is supposed it incentivize us into using them? Are concrete emplacements similar to Wehr bunkers?
They can be used as a weapon platform if you want to save a team weapon from being captured by the enemy. Also it can be crewed by a mortar and then used as a mortar pit.