Hairline on my CC hair is glitched and hairpiece glitches.

Hi. The hairline must be vertex painted with a different color
- select the hair, in edit mode select everything with A, Remove doubles;
- Select - select boundary loops, Select - Select more/less - More;
- switch to Vertex paint, enable Face selection masking for painting, change the color to 007F3F, Paint - Set vertex colors;
- press A once, then again to select everything, Paint - Smooth vertex colors
(you can see where the buttons are on the last frame)

Upon closer look at the file and the screenshot i noticed a few other causes:
1). In the shared file the hole is not closed while it seems to be closed in the screenshot above.
When you extrude edges and create a sharp edge loop like this, dark shadow appears along it. To prevent it, you need to tell the game to shade it as sharp by splitting it. Alternatively, you can just not close this hole. You won't really see it anyway
2). If you were to change the shading to solid, you'd see that the scalp on the hair clips into the scalp on the head mesh. To fix this, you need to select the edge along the (actual) hairline like in the pic and offset it a bit with Alt S. It will be easier to do this in the uv editor. For the future, when you're editing the mesh, try to avoid the hairline like a plague ( do not reshape or overwrite any of its data) or it will clip.

3). Also, the normal map is not done correctly, it should have grey background, not white or transparent. You can clone any hair and check its normal map to get what i mean

Can’t check the file at the moment but does the flower belong to the same meshgroup as the veil? If yes, just separate the flower and join it with the hair.