I don't see any zero temp poly resistors available. I don't know if both of those transistors are available at the same time. Someone from efabless could answer this.

The transistor models are BSIM4.0, so I count it as ok, as far models are ok https://github.com/google/skywater-pdk-libs-sky130_fd_pr/blob/f62031a1be9aefe902d6[…]6f59b57627436/cells/nfet_01v8/sky130_fd_pr__nfet_01v8.pm3.spice There are model problems for transistors outside the bin's strict sizes. The simulation works, but there are derivative discontinuities for W and L sweeps. No big deal. There are bigger problems than proper modeling of subthreshold region, such as parasitic currents to substrate, for example. If your circuit is good, you shouldn't be concerned too much about accuracy, anyway.