Can i make half-profile weldment profiles?
Meaning that can the sketches be half-profiles and still work, example: a circle of 50mm(diameter) cut in half.
Yes you have to create a custom weldment profiles. The default profiles can be found in program files> SolidWorks Corp> Data> Weldment profiles. Open a weldment profile, edit the sketch, delete whatever is inside the sketch and then draw in your half profile. Then do a save as and label accordingly. Keep in mind that weldment profiles are centered by the origin and the half profile may not be aligned the way you want, so you may have to change the angle of the profile to fix this.