[Imp]

Not sure but riders might help tank spot marginly better & will dismount & fire back.
A poor experience suppresed unit may be spotted by rider & tank before mounts attack so the rider could dismount & take fire instead.
Riding tanks into battle generally not a good idea better to have APCs supporting the tanks as eyes. The act of unloading from the tank means the tanks op fire that turn will be less accurate. Not 100% sure on that test if you like but think thats how it works. Best used to likely point of contact then have them dismount not in front line is my view.