Yes your beagle dog can sleep outside safely as long as the weather is warm enough and the beagle dog has proper shelter in the event of rain, wind etc.
If the weather is too hot or too cold then you should bring the beagle dog inside to prevent the dog from overheating or freezing to death.
No dog should be left outside in either the really hot heat or in extreme cold for too long because they can die just like humans can.
Even if a dog has a dog house they cannot stay warm enough to survive in freezing temperatures especially if the temperature outside is below freezing.
If you're having extreme cold weather you should always bring the dog inside the house to protect them otherwise they can die.
That goes for other dogs as well and not just beagles.