Quick Update.
Called Chase regarding using a spouse's OnePass account for the OnePass MC. Was informed to go ahead and leave it with spouse's OnePass account #.
Called Citi regarding using spouse's AAdvantage. Was informed it was OK as long as the AAdvantage accounts are "linked".
Called AAdvantage to link the accounts. Was told the AAdvantage account could not be linked. (I guess best to change the associated FFP# for Citi AAdvantage Visa & Amex to match primary card holder).
Called Fidelity regarding using spouse's MileagePlus account. Was informed that it is not advisable and that if the names do not match, the mileage would be "bounced" back. Was told to make a new account with the matching FFP# as CSR made a note in the old account.
Not sure if this helps anyway. Just some data point from my numerous calls this afternoon.