I have an iPod Nano from 2009 as well and yes I can record voice memos. It has the feature built in which is awesome. All you have to do is go to extras and click on voice memos and start recording. It's pretty cool and it's the same voice memo app that's in the iPhone so if you know how to use it on the iPhone then you know how to use it on the iPod Nano!!
I believe they can be long ones ... as much as the space you have on the iPod Nano itself. Although it might break them down for you. That's my experience with the voice memos.