You can get a cracked wheel welded. But it most likely will crack again either through the weld or on either side of it as the welded bit is stronger and creates a stress riser.
You can weld it and cross your fingers but with the experience I've had I would just buy a new wheel or change all four to a new style straight off the bat.
2007 E93 335i. Space grey. M3 19" reps. Matte black grilles. Lux V3. Cobb AP.