If you want to talk to a Nomad, you can greatly increase your chances if you
- Aren't Order, Core or other very hostile factions
- Are not a threat, i.e. not an armed ship of a class that would be a danger to them
- Aren't anywhere near their hives and aren't in any Nomad home system
- Maintain a respectful distance
- Make your peaceful intentions clear
If you do all that, there's a good chance the Nomad can be willing to roleplay. At least my K'Hara characters would be.
After all, the mindshare does want humans that are open towards them, whether to infect them or to use as "cultists" that try to convince other humans.