Vendor Account attribute in defaulting rule setup of Depot Repair

Hello,

Came across an observation and wanted to confirm if this is intended behavior. When we try to set up a defaulting rule with Vendor Account in depot defaulting rule setup page.See that Vendor account  LOV to show up vendor details it has to defined as a customer in customer standard only then Vendor Account LOV shows up the vendor details. Is this intended behavior. Shouldn't this LOV shows vendor account details if the vendor is defined as supplier in purchasing module.

Attached document illustrated with an example and screenshot.

Any insight on the above is really appreciated.

Regards