I have some old debts on my credit report for 2 overdrawn checking accounts. I plan on sending both the CA's a pay for deletion letter, but are CA's able to delete entries from ChexSystems as well or does the original bank/creditor have to do that?

It depends on who has reported it to chexsystems, If the bank has reported it which is normal, then no, they will not remove you. Sometimes paying the debt can result in being reported by chexsystems for a LONGER period of time

There is a set date that chexsystems will remove all negatives from your account. Chexsystems will remove all negatives after 5 years unless payment is made to the reporting bank(s) which could then result in being reported 5 years from the date that it was paid in full or the last payment was made. Example: If your report is from 06/2006 you would be removed by chexsystems 06/2011 but if for some reason you owed money to the bank that reported you and lets say you paid it in fill on 12/2009 , this could result in being reported until 12/2014 So this is why I suggest to those with especially older reports, NOT to pay them until AFTER THE 5 YEAR DATE. After you are removed and it drops off, if payment is made after that point, they can not put it back on chexsystems.

Of course you may stilll feel it necessary to pay off the debt due to other credit issues as you have already stated. Be aware that many people have reported being lied to by banks. Unless you get it in writing, don't count on it