I can tell you with authority that the most certainly DO NOT combine the spend on your personal and business cards.

There are two types of Centurion card:
1. Centurion
2. Business Centurion

in order to get number 1 - you must have the minimum 250,000 spend on any and all PERSONAL cards.

in order to get number 2 - you must have the minimum 250,000 spend on any and all BUSINESS cards.

If you have 200,000 of spending on your Personal Gold, and 150,000 on your Open (business) Gold, and 50,000 on your Open Platinum - you THINK that totals 400,000.

However - the way Amex views it is:
1. 200,000 on your personal card = DON'T QUALIFY for a Personal Centurion
2. 150,000 plus 50,000 on your Open cards (total 200,000) = DON'T QUALIFY for a Business Centurion.

I know of someone who had $240,000 spend on one type of card (and MUCH more than the remaining 10,000 on the other type) and despite pleading, begging, and finally yelling - they were NOT given a Personal OR a Business Centurion card. Amex says that they did not qualify for either of the two Centurion cards.

They usually don't make exceptions. I know of one case where there was over $400,000 of spend on ONE CARD, and because it was not the right type of card (e.g. a personal green, gold or plat and business/open green, gold or plat) they were not given a Centurion card.
Instead they were asked to start accumulating 250,000 on one of these six cards (or a combined 3 in the same category of personal or business/open) and only THEN would they be issued the Centurion card.

Without going into much detail, eventually a Director of Amex had to relax the rules and allow them to qualify for a Centurion card after waiting a few months of seeing spend of 50k+ monthly on one of the "six proper cards" and verifying their seven-figure checking account balance...

But that is the only such case I have heard of. Even existing Centurion Members (like myself) cannot bend any of their rules, nor can you get seasonal benefits you were not "computer-randomly-generated-invited-to" (like vouchers, presents, etc). Trust me, I have been there and done that - and know from first-hand and second-hand that they are very anal about this kind of stuff.