If you want to determine which variant goes into a given assembly, then a unique ID (Part Number) for each variant would be required. I'd recommend this as a best practise beyond Fit, Form and Function - think in terms of troubleshooting a failure and the potential for an unanticipated failure with material as root cause. If you do not differentiate between materials, you'll make it almost impossible to make the connection between failures and material differences.
From there I would use a Multi-Detail approach for the Drawing and describe all material variants with shared geometry on a single Drawing. Models could be Family Table Instances, (or not). Each variant could get a WTPart, but does not need to. Each variant would get a unique Item Number in your ERP (if you were using them, the WTPart would be equivalent to your ERP Item. This has the added benefit of ensuring that geometry (and other) changes get applied to all same-but-different Items.
Given the commentary around use of WTParts, my guess is that the paradigm is still one of "CAD as primary". Recommend a shift in thinking to WTPart as primary, with CAD describing the WTPart (digital representation of "the thing"). You don't have to start using WTParts as the approach is beneficial even in a CAD (Creo) centric environment.