Q: Is it possible to update the firmware on my first generation iPod nano to make use of voice recorders to record audio/voice memos?
A: Unfortunately, no. Current voice recording accessories are only supported on the second-generation iPod nano, iPod nano (with video), fifth-generation iPod and iPod classic.
The fourth-generation iPod also supported voice recording, but used a different type of recording accessory.
iPod firmware replacements such as Rockbox offer some voice recording capabilities for otherwise-unsupported iPod models, but these are complete replacements for your existing iPod firmware, and are recommended only for advanced users who understand what they are doing.
Some compatibility with iTunes will definitely be lost in the process, and not all of the iPod’s other built-in features have necessarily been ported to Rockbox. Further, not all existing recording accessories are necessarily compatible with Rockbox.