You would still have guidence.

Autosteer on a 2wd tractor should be possible as the tractor will run at a much lower speed even if the monitor is expecting the steering response of a sprayer. Like you said it is very likely that some adjustments to the NAV2 settings may need to be done. Autosteer on a 4wd may be more complicated to tune but I have never tried.
 
If a guy has no Accuguide in his applicator tractor then he has no reason not to use his Pro600/700 to control product and provide lightbar guidence.