BTW - I would be interested o find out which drives Glyph and OWC use in their externals, not just the manufacturer but also the type of drive.
It's irrelevant.
When you purchase an *external* hard drive you are putting your faith in the company that puts together the final product, not the company that makes the internal mechanism.
External hard drive manufactures don't usually use the same consumer-grade internal mechanisms as you and I can purchase at retail (even when their internal mechanisms have the same name as a model you can purchase via retail). They work with their supplier and request drives of a certain performance, and tested to a certain level of reliability. Then, if the company is really concentrating on reliability (e.g. Glyph), they test every single mechanism they receive and reject those that don't meet their standard.
Then they put the internal mechanism in a case that offers a particular compromise between keeping the internal mechanism reliable, performance and price. If you look at a Glyph external hard drive, you can instantly see and feel that it's built like a tank. It's heavy, it has a huge power supply, and it has a fan to make absolutely sure that the internal mechanism is always kept cool (heat is the natural enemy of magnetic media). Other manufacturers may go cheaper and use their external drive's metal case as a heatsink, and some offer almost no cooling at all.
You'll notice that, of the three brands/models of external hard drive that I recommended, there is a very obvious visual correlation between how robust the drive looks, and price. That's not an accident. Of the three external hard drive brands/models that I recommended, the more expensive you go, the better made and the more reliable they are.
So, the internal mechanism inside any external hard drive you purchase makes no difference. What's important is the manufacturer's dedication to quality and reliability. Even Toshiba, a company that generally makes very good internal hard drive mechanisms across the board, cheaps out on the cases for their external hard drives. Both Western Digital and Seagate make some superb rotating disk hard drive mechanisms, and some putrid ones. Sadly it doesn't matter how good the internal mechanisms are in WD's and Seagate's own branded external hard drives, both companies put their own mechanisms in putrid cases, and so their external hard drives are garbage.
To answer your question directly, both OWC and Glyph spec their internal hard drive mechanisms from Seagate...mostly. But as I said, that's irrelevant. What *is* important is that Glyph, Novus, and OWC are all known for quality and reliability within their respective price points. But the three are far from equal.