Preferably not.  Although purchasing reservations in the consolidated billing account has the advantage of simplifying the purchase and management of reservations, because reservations have the ability to float through linked accounts, you may not be able to launch a reserved instance in the same account that you purchased the reservation for.

The best practice is to purchase reservations in the accounts in which the attributes of the reservation match the running instances that will be utilized in that account.  By purchasing reservations in the linked accounts, you ensure that the discounted reservation rate are applied to the desired instances within the desired account.