If you're talking about actually building a vest, don't do it. It's not worth the risk of severe burn. Ditto for the motorcycle heating vests that are out there. There are plenty of other options that really don't cost that much. But I'm still confused about the E/O question. The standard E/O connection (yes, Jon Nellis, I know these are not really E/O connectors) is outside the suit between the bulkhead and the battery. The connection between the vest and the bulkhead is inside the suit and is different for each vest. It doesn't need to be standardized, and it doesn't really need to be waterproof since it is inside the suit, but caution is advised in case of a flood.
The least expensive combination inflator/bulkhead I know is the one from Golem. I use that one with my Santi vest because the Santi bulkhead was crazy expensive. I just clipped off the LOLA connector it came with and soldered on the Santi one, using waterproof heat shrink tube to finish it off.