Feasibility of flashing a ROM (meant for original device) on a re-branded device
If all the specifications match, including chip level and GPU Mali blobs, it sounds a reasonable try, though I never owned a re-branded device.

After taking complete backup including EFS and double checking, I would suggest first flash the kernel from the proposed ROM to replace the existing kernel. If it boots properly and basic functionality of phone is fine, then you can flash the complete ROM. This way you are ruling out kernel compatibility issues.