They can but whether they should is a different question. There are two main considerations when it comes to leaving a lab to live outdoors 24/7 – 1) will the dog be able to tolerate the temperature ranges in your area and 2) will the dog be lonely or is there going to be enough socialization and playtime for it every day.
The latter is a matter of personal circumstances but the former is very much a numbers game. Labs need a safe temperature range of 50o to 80o F (10o to 26o C) to be well and healthy. If the temperatures in your area go below or above that you’re going to have to make sure that your dog has access to a well-insulated and heated/air-conditioned dog house.