The short answer is definitely not.
Low tech tanks often don't have fertilizers added to them, and certainly not CO2 injected. It depends on who is defining low tech, some will say DIY CO2 counts as low tech, but others (like myself) are of the feeling that any added CO2 is not low tech.
Not adding ferts or CO2 changes to some extent what plants you can grow, but if you look at the low tech can be lush too thread and low tech plant list you can get a good idea of what plants work well
A good place to start is with java ferns, anubias, cryptocorynes (crypts) (many varieties of all 3), and bolbitis.
Personally, my tanks are all super low tech. Crypts get most of their nutrients through their roots so now that my planted tank substrate is getting old I do add root tabs under the crypts about twice a year, but otherwise I rely only on the fish to provide fertilizer for my plants. I also keep my tanks on the slightly overstocked side to keep the plants happy, but because the plants do grow well, the water parameters are always excellent, so the fish are happy
I got into planted tanks to make the fish happier, so it's definitely important to me that the tanks are stable and parameters are good.
So again, no it is definitely not necessary to add fertilizers (caveat...once your nutrient rich substrate gets older you may need to supplement with root tabs occasionally for heavy root feeders like crypts...if and when this becomes necessary will depend on what substrate you use, for example I've heard mineralized topsoil type substrates don't last basically forever). And you definitely don't need to add CO2.