When you apply nematodes you do it in a soaking manner, they can't live on the surface of the soil for long - so when the ground is moist, (water first if you have to), or right before a moderate rain. (half inch or so - when it will soak in, not run off).
You aren't penetrating the soil when spot treating with the tobacco juice - your fertilizers are organic, so no, I don't think what you are using will kill them.
Our droughts are why I have to reapply my nematodes - I don't water my perimeter areas at all - and the fire ants come in there. But I do still have pretty good protection in the areas I garden and therefore water, after a year or 2, sometimes 3. It is cheaper to reapply nematodes than to keep the edges of the lot watered all summer long.
(and by the way, have you got an easy cure for aphids? I was going to use dilute dish soap on my pear tree leaves - I have removed the tiny black ants that were farming them from a hideout in a fold of pond liner)
Time to be a gypsy again, 2014 will be my prep year, my bees want a better area with actual rainfall.