This should be no problem - that is to say it has not been a problem for me. In a 'household account' your wife (or whoever)'s account card is linked to yours and your on-line history will show your transactions only - but also the total of the linked accounts. This pooled total is then available for use with Amex vouchers.

The bit I have never worked out is how BA allocate the redeemed miles between the grouped accounts - but that is another story,