See my sibling's comment about lanes and medians, but in general, yes.

In fact, a school bus with red flashers on is, in my state, passing it is the only thing we cannot do in an emergency vehicle (in my case, ambulance and fire engine), even in "emergency mode" (lights and sirens both active).

I've only ever had this happen twice though, and in both cases the bus drivers stopped the process and turned their lights off for us.