A central obstruction should be no problem. Obviously if the obstruction is very large you will get dimmer spikes. A mask that is in two pieces (I assume you mean that when you say 'split mask') will not be a good idea. The angles involved in a Carey mask are such that any error in getting the two halves fitted together will destroy the accuracy. You judge focus by comparing the very narrow separation in left/right spikes and a fraction of a degree error would make this impossible. This would also apply to the Bahtinov mask.
If the two halves were cut precisely and fitted together without any gaps then it could work. Perhaps..
