SW actually had a similar discussion some time ago and Chris (formerly Chris from MS -- who was always extremely helpful in answering licensing questions) replied in no uncertain terms that this is not a valid method of receiving a LEGAL license of Windows 10. There are also several comments noting the part in Microsoft's EULA that essentially states that "a successful activation in no way denotes legal entitlement". While Chris is no longer an employee, he's the closest word we have to a statement from Microsoft directly.
Having been a witness to a Microsoft LLC audit that I mentioned previously (where upgrades of Windows 7 PCs without 10 entitlement in MSDM/Bios/whatever performed after this date were listed as "unlicensed" (EDIT: I do not know the outcome of this, only that these were initially listed as the above but may have later been amended further into the audit process), with the careful wording around the EULA, with the blatant statements on their website, and numerous other MVPs and MS insiders stating that this is the case, I choose to err on the side of legality/compliance when we're possibly placing a client at risk.
Personal PC? Go ahead, I don't care.
Business PC? Buy a license and know you're compliant.