I wouldn't break up owners and vendors. I'd say whether it's a reference to a vendor or owner is an attribute of the reference itself. It may be seldom in your situation, that an organization is a vendor and an owner, but generally organizations produce somethings and own things of produced by other organizations. While you only put into your database what you own, the concept of organization types is only reflecting your view.
Of course a software vendor is a software vendor, but it can (and should) also own hardware to be able to produce software.
So I'd put the references of resources to organizations in a seperate table:
otpType (Vendor | Owner | etc)
addType (Billing | HQ | etc)
The ResourceOrganizations table then maintains all the references towards organizations involved with the resource, which can be more than vendor and owner. There can be the disposer, the shop it came from or it's repaired at etc.
Even if you just and always maintain exactly two relationships to an owner and a vendor this is possible this way. And I introduced a mainType in the Organization table to specify the main type of an organization, eg perhaps in your case Microsoft mainly is a vendor of software you own and so it's the main organization role.