Yes, constructions of the type “ce n’est pas X”, X being a superlative, are commonly used to convey irony. In particular, there is an idiomatic expression “ce n’est pas un foudre de guerre”, which is employed to mean that someone is not exactly smart, fast or powerful. It draws from the older emphatic expression “un foudre de guerre” (an extraordinary military man, or forceful man of action), which is not really used anymore except in this construct.

On the other hand, I feel that the common use of this construct robs it of its irony in many case, and is nowaday simply used as a way to express one’s negative view of something without using a strong pejorative. For example, “il n’est pas très à l’heure” is somewhat more diplomatic than “he was quite late”… As another example, my 3-year old son says sentences like “ton camion il n’est pas très beau”, and though he uses it the right way, I’m not sure the irony is not lost on him.

This rhetorical device is called litotes, and it works the same way in French as it does in English.