I'm a type 2 diabetic on insulin(during pregnancy only), and was when I first VBAC'ed 2+ years ago. It depends on your provider, some of them think as long as the blood sugar is controlled, you aren't really any different than a regular lady. I was subject to more monitoring, such as the non stress test and biophysical profile (bi-weekly now that I am 36 weeks). Some providers don't want you to go past your due date if you are GD/DM because it slightly increases the risk of stillbirth. My OB is ok to wait as long as the tests are good and the kick counts are good but you will probably need to talk to your provider to find out what their oppinion is. It does put us VBACers a little on the spot if they don't want us going over yet they won't induce us b/c of rupture risk. Your baby might be subject to increased blood sugar monitoring when it is born, especially if large for gestational age.
Don't think having prodromol labor decreases your VBAC chances. At least it's a sign your body is getting ready! Tell baby to wait till at least 37 weeks though ;-)