Both projects want to replace BibTeX in a way but with different goals. Searching for both search terms at the same time is a rather frustrating experience. Is there any mutual recognition at all? Can both be used together? Does the roadmap for Biber development aim to include the functionality NbibTeX provides?
They aren't really comparable. Biblatex+biber vs NbibTeX is a better comparison as the features of biblatex+biber are possible because the different tasks are parcelled out to engines with the most appropriate capabilities. Biblatex+biber do a great deal more than BibTeX or NbibTeX. NbibTeX allows users citation "keys" to be essentially a match on bib data. I've considered that for biber but I've never been convinced of how much use this is - when you make a document, you just want to point to exactly the entry you want, not search and hopefully, or even likely, get the right one. You just want the right one. Biber allows multiple keys for the same entry to get round some of the main problems with passing
As far as compatibility, I suspect you can use NbibTeX as a drop-in replacement for BibTeX when using biblatex. However, most of the best features of biblatex require biber and won't work with any other backend.