I'm confused between two vias: nw-to-M1 and rx-to-M1. I figured the first one is from nwell to M1 and the second is from active layer to M1. Looking at two vias in the layout, the only difference is that nw-to-M1 has an extra surrounding nwell compared with rx-to-M1. So if I put rx-to-M1 in a large nwell, is it the same as a nw-to-M1 via?
I don't know the IBM PDK, so I'm not sure about the rx layer. If it's a poly resistor layer, then it's a surface layer as well as nwell, so a contact to M1 is ok.
If such a poly resistor on nwell is modeled in your PDK, that's a different kettle of fish. At least you should know its resistivity.