NSF postdoctoral fellowship eligibility requirements
The eligibility requirements are stated in the solicitation.  It certainly sounds like you will be eligible.  If you defend in spring of 2015, then you can apply in falls of 2014,'15, or '16 to start the following summer (in fall 2017, it will be too late, since you will have had your Ph.D. for two years on Jan 1, 2018, and 2018 would the "year of the award). The only things that can make you ineligible are: losing your US citizenship (presumably easy to avoid), serving as PI on an NSF grant (again, not a huge danger), and being offered the fellowship and turning it down.  (I think there is also some general stuff about drugs convictions, etc.)  

Taking any kind of job will not make you ineligible, though it's possible it could influence the way your application is looked at (for good or for ill, I can't really say).  You can apply with your current job as your site, or with a different one.  I don't know many examples of people getting the fellowship after they first graduated, though of course, 2015 will be when you first graduated, so maybe that's not an issue.

Just a general comment: if you have questions about NSF awards, ask the program director.  They'll be the ones who actually interpret the rules, so they know better than random people on the internet how they'll be interpreted.