Cucurbits are definitely not as hardy as tomatoes or peppers, which can withstand nights in the 40s. While it might stunt growth during that time, they're able to get their root systems established to get ready for big growth once the average highs get nearer to 80 and nights generally don't get below 50.
I generally wait to plant cucumbers and cantaloupes until we're well into May, but tomatoes and peppers go into the ground anywhere between April 20 and May 5, depending on the long-range forecasts.