Can a man wear a dark suit instead of a tux to a black tie event?

It is generally a bad idea.

Some invitations will decree "Black Tie Optional" or "Black Tie Preferred." At the former, tuxedos will probably be worn by the majority of men, but a dark suit is acceptable. At the latter, a dark suit is narrowly acceptable if time or finances truly prevent a man from even renting a tuxedo. However, if an invitation simply says "Black Tie," it would be impolite not to wear a tuxedo.