In my early learning stages of installing a front hub on suspension forks, taking zinc nuts on and off repeatedly using adjustable spanners I gnarled up zinc nuts real easy, from outer wear to cross threading, so I invested in titanium nuts and found a huge difference in quality and would recommend them to all those starting out on their conversion kit journey.
One of titanium's weakpoints concerning the grade used for fasteners is its low fatigue resistance. When used in race cars and things like that, they're used as one-shot fasterners, i.e replaced if disassembled. Also. they're very prone to galling, especially if the thread is cut rather than rolled, so you'd be advised to put some lubricant on the thread before tightening. Maybe that's another reason why they're replaced rather than reused. In summary, titanium has problems that can catch out the unwaray, while as zinc plated mild steel nuts are suitable for any ham-fisted ebiker.
All the motor manufacturers supply zinc plated nuts as standard. They're on all OEM ebikes with hub-motors. I've never seen or heard of a problem with them in 11 years of working with/on ebikes. They're stronger that stainless steel. I'm not sure how they compare with titanium, but IMHO that's a completely unnecessary expense. Buy titanium to save weight or because they look nice.