Is it normal to have a gap in my gums between the sides of the incision after a particulate Bone Graft? (photos)

It may be nothing, it may not.  If the membrane is a certain material, it isn't a big deal and is designed to be exposed.  Not all membranes are like that.  The best judge is the surgeon that DID it, so give them a call.

Although it looks like the gingiva is exposed, that does not mean there is an infection. It could be just exposure of the materials that were used in regeneration. If there is any doubt, as always, I would suggest you visit your specialist to confirm. 

Without examine it would be difficult to say anything. So you should visit your oral surgeon to fix it.