Hi Sameer,
The AD8237 has a different internal architecture compared to earlier instrumentation amplifiers. The earlier in-amps have a 2 op-amp or 3 op-amp architecture, both of which have two stages with different gains to the output. This is the reason why they need to have Eni and Eno specifications.
The AD8237, on the other hand, will generate noise internally just like an op-amp. The voltage noise referred to the input should remain constant (refer to page 3 of the datasheet), while the voltage noise referred to the output will just be the specified voltage noise multiplied by the external gain applied. Generally, calculating the noise for an AD8237 circuit which uses passive components to set the gain will be the same as calculating the noise for an op amp in a non-inverting configuration.
I hope this helps!
Kris