Does a NIOS II need reset?

Not sure what you mean by that since you figured out the NIOS core will not function without it.

Pretty much any processor needs a reset so that it starts at the correct reset location (if you power up a processor

in an undefined state, you don't have a clue how it could react in some situations).

Also keep in mind the symbol you are looking at on the screen in your block diagram is not just the NIOS processor in, but

the whole SOPC system. Removing reset logic from the rest of those devices is not a good idea for two

reasons: 1) you will not know their behaviour since they are not your core 2) designers don't put in resets for no reason

at all.