I think I found a solution.
t2 root I was able to SSH into the Tessel. From there I found that there is a unique machine id in the file
/var/lib/dbus/machine-id. And using Node's
fs.readFileSync() I am able to get a unique device ID.
var fs = require('fs');
var uidFile = '/var/lib/dbus/machine-id';
var deviceId = fs.readFileSync(uidFile).toString();
Hope that helps anyone who's looking for a unique hardware id in Tessel 2.