Yes. You need to etch the part after any machining, unless otherwise specified in the drawing.
Nital etch has nothing to do with "grinding" per se; It is looking for any heat affected zones on a hardened component.
Grinding is simply a "high heat" process prone to burning, so etching is typically used to verify grinding ops.
These "burns" can be created by any type of manufacturing process. Milling, turning, drilling, polishing/deburring, etc.
It is wise to etch after machining a hard part.
J
NX 6.0.5.3