SirsiDynix was setup to block the placing of holds on expired patron accounts. Polaris is not configured with this restriction. If an expired patrons asks to have a hold placed for them (via phone, email, or whatever), place the hold but remind them that they will need to renew their account before being allowed to checkout materials.
Keep in mind, that this does not apply to ILL requests. Because of the time and expense involved in obtaining items from other libraries, patrons need to have active accounts before requesting an item via ILL.