nezirus - nidrei gavoha or nidrei bituei?

I thank Anonymous for pointing me to a letter the Rav wrote to R’ Hutner upon receiving advanced copy of R’ Hutner’s Toras Nazir – see Igros haGRI”D p 278. The Rav addresses the question of which box – nidrei gavoha or nidrei issur – a neder of nezirus fits into. As we have seen earlier in the week, the Ramban defines nidrei hekdesh and tzedaka based on the hischayvus, the obligation such a neder creates. Nidrei bituei do not create a hischayvus to do something, e.g. giving tzedaka or offering a korban – they create issurim. At first glance one would suspect that nezirus is a form of nidrei gavoha, as one who becomes a nazir accepts the obligations of bringing the korbanos of nezirus. However, the Rambam opens hilchos nezirus with the statement “Hanezirus hi neder bichlal nidrei issur”, nezirus is in the category of nidrei issur! The Rav explains that the neder of nezirus is not an acceptance of korbanos obligations, but an acceptance of the shem nazir. Once one is defined as a nazir, it naturally follows that certain obligations stem from that chalos.