To answer your question let me descibe how we receive VM properties. Our solution includes a collector which connects to vCneter or ESX(i) host and retreive all necessary information. Then SCOM agent should process received configuration to create your virtual topology in SCOM. We have to be very carefull with what we collect and publish to SCOM agent, if there is too much data, operations manager agent may fail to process it in a reasonable time. That's why we extract only necessary properties of virtual machine. However we always wanted to have a flexibility of collecting extra information which can be specified by a customer. That's why we have these custom tags functionality.
With respect to your situation, please correct me if I didn't get your point correctly - you have certain properties as custom attributes of Virtual Machine in vCenter and you want to get them in SCOM and SCSM, right?
In this case I'm afraid you have to rename your properties to Veeam.CustomTag1, Veeam.CustomTag2, etc. These are the only custom attributes our collector extracts and publishes for SCOM agent(due to performance considerations). Once you renamed them - everything should work automatically - collector is already collecting them, but when you put your data there - they will be published for the agent, then the agent will automatically collect custom tags and you will see them in SCOM as CustomTag1,2,3 properties of a virtual machine.
You can also create a custom attribute with friendly name in SCOM and you can even get the same custom tags from WMI (VMProperties.customTag0,...), but I would not recommend this - such a customization will create and additional(extended) class for a virtual machine and some native Vmware views maybe be broken because of that. Maybe if you are using SCOM as a "service layer" between VI and SCSM this may work.
Let me know if you have any additional questions about using custom VMWare tags in SCOM.