What are the units of Es/N0?
The "symbols per second" (or, more strictly, the baud) unit is a bit weird. It is really a unit that is used for human convenience and not for mathematical rigor. Just like "samples per second", bauds can be interpreted as hertz and still make sense, since they measure the "number of times something happens per second".

So, in your calculation, the units of $B/R_S$ are $\text{Hz}/\text{Hz}$, making it unitless.

I know this is somewhat unsatisfying (at least, it is to me), but this is the best explanation I can give.

(All your unit definitions at the top of the question are correct, BTW).