I am not sure if I would be adding nematodes, they need quite warm, humid and very damp conditions and feed mostly on humus.
They are actually parasites and I would be hesitant of anything parasitic to the soil of my babies.
Seeing the conditions they need to do their best work is basically a tropical compost heap, I doubt they would benefit your indoor grow greatly.
Never the less, it could be an interesting experiment and until you try, there is no way of knowing the results. Results may be hard to quantify though, unless you grew 2 plants of the same strain (preferably clones) side by side and had nematodes in only one pot, but everything else was identical.
I think that if any great benefit were to be had by adding nematodes, the cannabis community would be well aware of the fact already.
If adding nematodes, I would suggest giving them a week or so to become established before adding any fertilizers. They are no doubt fairly fragile creatures and strong fertilizers would probably not be their best friend, since they live in a fairly nutrient poor environment in nature.
Hope this helps,.......
Organoman.