I’m using a 0.6 diamondback, and some 0.4 bimetal CHT nozzles. So yes you can use third party as long as they are MK8 style. You can also mix and match with the various sizes (IE 0.6 nozzle on the 0.4 hotend), but you will get an annoying beep and dialog box that pops up asking you to confirm when you start the print. Which is better than before when it straight up wouldnt let you print at all if the Gcode did not match the installed nozzle.
TL;DR Yes you can use any nozzle you want as long as it is a MK8 style
The 0.8 nozels they have shipped are ambitious at best, its not a high flow system in my opinion. You might want to look for options 0.6 and bellow. Anything more and you have to slow the print speed down so much it doesn’t actually save any time.