I wear my hair system in a central parting and it's been fine. I now have a custom system, all swiss lace, roughly 10 - 12 inches hair length, medium light density, freestyle hair direction (combed into a parting), medium brown colour (#5 on the colour scale). If the density is thick enough, you don't really notice the knots in the lace in the parting as it ends up not being too wide and therefore not too much 'scalp' (lace) shows through. As others have said, though, ideally you might like to bleach the knots in that area or do the 'dyed after' thing in a custom order to get even more realism.
There a few other things you can do to make the knots less visible on a parting, based on my own experiences. I would try not to make the parting too wide or too perfect in terms of how you comb it. Of course I do like to get my parting straight and positioned down the middle as accurately as possible, but I try not to make it too much of a 'hard part' if that makes sense. I also slightly criss-cross some of the hair on each side so it looks more realistic - instead of a really hard part exposing lace, it looks more like hair naturally growing out of my scalp.
I saw on the Hair Direct website that there's also a difference between a central parting and a central break. A parting exposes more lace, whereas a 'break' is where the hair is combed into a parting but still has hair density in the parting area, thus not really exposing the lace. You can get away with either, though.
For my next custom order, I'm planning on asking for either bleached knots, skin or 'dyed after' for the parting area, but I can live with it as it is for now.
One warning, though - if you wear your system for many months, the lace in the parting will eventually become more visible due to the shedding. This can be fixed temporarily by using hair fibres or hair loss concealer powder, but ideally you want to replace your system before it gets too bad looking.
There are some other tricks you can do to hide the knots in a parting, for example applying foundation cream or powder onto the top or underside of the parting, the same colour as your scalp - look up some Youtube videos of women, especially black women, who do tutorials on this as they are really good at that stuff.
A central parting also has the advantage that it can be used to help line the system up on your head while attaching!