I’m actually working for an OEM vendor and therefore had to use Microsoft OEM ISO images. One or two things undocumented on the web makes me loose some times, so I've written them down here, hoping someone else can take benefits of it.
Naming convention
For some reasons OEM images that are available on the Microsoft purchase site are all prefixed with the “IoT” name…
…which surely means something meaningful but who is actually more confusing than anything else if you ask me. To quickly finish with this one, the answer is YES, you can safely purchase them, it’s definitely the regular windows images you are used to, and YES, they have nothing to do with Windows 10 IoT (the internet of thing edition)…
Image format
Once your Windows SKU is purchased and downloaded you may fall on uncommon ISO format like .IMG or .DAT. IMG is used for images below 4 GB and can be red directly by Windows 10, DAT is for images above the 4 GB limit an can be red by… nothing… I had to ask the living OSD internet database a.k.a Michael Niehaus who suggested the rename the file to ISO to use them… Thanks to him that was as simple as that… almost…
Split DAT Files
As I said, DAT files are for images bigger than 4 Go and are delivered in the form of two distinctive DAT files that you must join together before renaming to ISO. If you are not that kind of guy that join files every day, I can recommend using a tool called File Joiner. Once the job is done you should be able to mount and use the image with your favorite deployment tool.
Key take away
OEM images are rigorously (to the bits) the same as the one you can download from your MSDN subscription (Except that you must rebuild them yourself… You are an engineer, don’t you ?). The only thing that really matter in the download package is the Product Key that is specific to OEM. So pick up the key, forget about the OEM ISO and use your regular one from MSDN and keep forces for more valuables topics… End of Transmission!