I'm working in a project that use nhibernate as orm. Is there any benefit for me to use sharp architecture? what is these benefits?
Mostly, the benefits are that a few conventions that support domain driven design, dependency injection, and loosely-coupled architecture are pre-wired for you so that you don't have to give as much thought to how to accomplish some basic things that would likely result in boilerplate code, false starts, and distractions.
Concrete examples of usefulness: The reasonable base class for a generic repository and a pre-extracted generic repository interface, an overridable but pre-written hook to a sensible dependency injection mechanism, an attribute based unit-of-work transaction scope, some additional model validations that you won't have to write yourself, just to name a few.
There are good arguments for some different choices than SharpArchitecture made, but if you don't have a strong justification for approaches that are dramatically different than SharpArchitecture puts in place for you, you can get up and running quite a bit faster than if you had to implement everything SharpArchitecture has already done.