Yes, DUI checkpoints are legal.
That could have made for a very short post, but allow me to expand by explaining why DUI checkpoints are generally legal. (I say generally because there can still be situations where a particular DUI checkpoint could be found illegal. Not all roadside sobriety checkpoints are necessarily set up and administered in a constitutionally permissible manner.)
Nevertheless, courts in the majority of states have upheld DUI checkpoints against challenges that these checkpoints are unconstitutional. Interestingly, courts have not upheld drug checkpoints.