Anyone here know if not having a product type with listed products will result in no inclusion into google base? My best guess is no but I would like others' input into the matter
I don't think so. Because of the product type must be listed. I could be wrong but that is my 2 cents.
I would make your product description as complete as possinle, meaning you should include the product type. You will not only get more traffic, but better traffic as well. You want the customers, not just the window shoppers or casual searches. To minimize the worthless traffic and get what you want be as complete as possible. You can only do better with that mindset, not worse.
I'm sure you can do worse if there is no suitable category and the product is misplaced. I might be better not having a category if it doesn't fit.
GMC's knowledge base says you can create your own PRODUCT_TYPE, but I've always used their presets. My sites all have 8000 - 50,000 products and in late 2009 I started to have more and more trouble getting new sites/feeds allowed. After extensive testing and validation of my feeds, I'm suspicious that GMC is currently automatically disallowing newly purchased domains. All my 4-year old domains have no problem.
You'll get listed, but not providing this field and any other field that is recommended by Google is shooting yourself in the foot. If you can provide the product_type, I'd make every effort to include it in your feed.