Today it’s not possible to hide a Part sub-type for a specific role within a Part Product Structure. When a user does not have permission on specific version or Part type the product structure will show the Part Master of that Part!
Example, if you have a BOM structure with 2 different part sub-type and that you control the Access policies to deny access to a specific roles, to a specific Part sub-type. The user within this role will still see the Part information thru the Part master within the Product Structure as below:
I think we should be able to hide any part including the Part Master from the Product Structure.