If trained properly, YES, these pups know how to detect blood sugar changes in the body.  They can detect the changes and alert ahead of time, as well as when the numbers get to the range of alert.  If your breath is outside the cone of scent, your DAD may not pick up the changes.  If your blood sugar remains low or high for a long period of time without changing, they may not be alerted because they smell the change.  They are sometimes 30 minutes ahead of time, so don't think they are wrong, we told Shugga "Let's Watch It", as he was most often early.  As a double precaution, I wore a Dexcom G6 and did the entire time I worked with Shugga.  It's good to see the ups and downs, and Shugga was always ahead of the Dexcom in letting me know.

If possible, visit the training facility ahead of time.  See how the training crew works with the dogs, the environment they are in and the care.  I would also suggest reading reviews and talking to those that have DADs from the facility to inquire about their experience, training, and how they worked with them as a handler team.  It is best to visit the facility as often as possible and see if they can train you with your pup while they are growing.  Each facility is a case by case scenario, and to be honest, a 1:1 trainer that the dog lives with and works with would be the most ideal setting, as they have hands on work and experience an environment, like they will be living with you.  Shugga had high levels of anxiety in transitions and public settings that we worked on for a number of years. He did the work and didn't show his stress too much, yet pulled more than needed due to his anxiety.  It is best to have a calm and relaxed service dog that can handle moving with you in all environments, and this may take work on both you as a handler and you and your dog together.  Don't get frustrated, there are many ways to calm your dog and slow them down with you. 

This topic was probably the hardest one we faced as a service dog team.  I was taught that there should be no interaction with anyone outside of Shugga and I.  Family and friends found this tough and it quickly became a drain and I felt awful telling people "no".  Shugga was the cutest thing and service dogs are so exciting and everyone wants to interact.  I will say it is best when you are a new "team" to follow the guidelines of your training facility, yet what I learned was, Shugga was driven by food and we could let him interact at times and still keep him in the realm of "action".  I let the reins up a bit later in his life and it was a nice balance, and to be honest I could have done it more earlier on.  If you're an all or nothing person, this may be a challenge you face.  It is best to decide how you will interact and be open to how you want to create that space for you and your DAD as you are together over the years.  Trust me, everyone will give their opinion on how you "should" let your dog interact or not, and whether it is fair for the dog to be working all the time, etc.  I did let Shugga play and I also listened to what people shared and made decisions that I took responsibility for.  I would suggest keeping consistent, whatever you choose.  And good luck, as this one can be answered in so many different ways.  I followed the ADA rules in public for the most part and appreciated those that respected the service dog rules too.  Again, it comes down to you and your DAD and how to keep them in the best space for the workability of you both.