Yes, that is retail Builder's OEM which comes with a COA sticker to affix to the machine showing the Windows 7 intstalled on it is genuine.
It is meant for System builders. What you are doing rehabbing and reselling PC's most likely qualifies.
OEM has in recent years been sold to anyone, even without the qualifying hardware purchase that was once required.
Your intended use is closer to what is intended according to this quotation of MS rules for OEM strictness.