I generally don't leave dogs together unsupervised unless they're both mine, in my house or a safely enclosed area (safe from escaping dogs and from dog thieves!), AND they have been living together for several months and I trust them with eachother.
It's fine to leave him in a crate or other safely enclosed area as long as you can come home sometime in the middle of the day to take him out. You also need to give him lots of playtime and mental exercise (fun, short training sessions and/or Kongs) How old is the puppy you're planning on getting? A slightly older puppy (4 to 6 months) might be easier with your schedule since they have more bladder control than an 8 week old. It is important that once you get home it's all about the dog though; take him out, play with him (teach bite inhibition), walk him some (at least start getting him used to having a leash attached to him and let him drag it around the house), and mental exercises. A few 5 to 10 minute training sessions with lots of praise and treats/toys a day are great for young puppy (under 6 months), as well as stuffed Kongs or similar toys.