For SUMA there are properties that can be modified to add any custom "Source" values to identify what values are Buy or Single Source
com.ptc.windchill.suma.oemPartMultiSource=buy
com.ptc.windchill.suma.oemPartSingleSource=singlesource
We had played around with adding some additional Source Values, and we saw no issues with it. In the end it didn't meet the business need so we removed them.
With ESI, you map they type to the corresponding ERP ID. Since we didn't proceed with adding any additional values, we didn't test the impact to ESI.
Source.make.*.*=1
Source.buy.*.*=2
Hope this helps,
Steve D.