Well, sorta.... the amp actually has an intended operating load range... some amps are rated to handle only down to 8 ohms, others handle down to 4 ohms... the better (and most expensive) handle down to 2 without problem........
When you say "the amp is rated at 4 ohms..." it generally means "the amp will handle as low as 4 ohm loads..."
To complicate it further, these aren't even absolute numbers (because these values are nominal or "averaged") -- actual load varies according the frequency of the signal being reproduced!
So anyways, it's not so much a question of matching the speaker and the amp in as much as it making sure the nominal (ie, rated) speaker load isn't lower than what the amp will handle..........