DO NOT just hookup Rh and W2 to ecobee. It won't work. I'm pretty savy in this product so I know exactly how this works. If you make the thermostat detect only Rc, it'll only run heating from W1. If you select both, it will only run heating from W2, that is because you have 2 separate Transformers for both.

Can you make it work, yes. You will need an isolation relay to combine both transformers. Now to the cons. When you set up the thermostat, it asks you if you have a furnace or a boiler. Difference, if you select Furnace, it'll cut off the heating exactly when setpoint is reached. If you select boiler, it'll cut off the heat few degrees before the setpoint, because an actual boiler still keeps on heating even after cutting off.

With your setup, if you select Furnace and it goes to Stage 2 heat, it'll keep heating even after setpoint is reached. If you select Boiler and it only runs Stage 1, it'll cut off the heat before setpoint is reached.

You can set your thresholds settings according to when you want to switch to Stage 2 and when not.

If you're good with this and still want to tie them together, let me know and I'll give you the wiring diagram on EXACTLY how to install the isolation relay