I think you'd need another protocol/product for that. Samiz syncs messages via Bluetooth, and Samiz is the agent that finds each other and communicates and then publishes to your local relay. Meshtastic syncs over a different long range radio frequency, but there isn't an app that takes messages and publishes it to a relay or vice versa. Also, Meshtastic is low bandwidth, so it is not good to send lots of data through it as you'd be hogging the bandwidth from everyone else. It's really important that it is used sparingly so you'd want to be selective about what messages you are sending out based on some sensible rules.

FYI, Samiz tries to be as efficient as possible, but I think a Meshtastic based system would need to also include thresholds and throttling on top of all that.

As experiment it's closer than you think. I just need to build a PC/raspi version of Samiz and tryout an already existing plugin for Meshtastic to connect to nostr. I'm not sure about performance but the Bluetooth technology used by Samiz is also low bandwidth. My point is that Samiz was built with this mind. I would love to, at least, give a try.