Dad has horrible credit...will putting my name on his checking and savings hurt my credit?

Don't do it. If he has debts that are actively being collected, it wouldn't take much legal work for the creditors to attach the bank account and get any money in there, even if it's your money. If your money is in the account it takes a lit of work to show it's yours and get it back. And the same goes for him too...if you have creditors they could take his money for your debt. Why not get him to an attorney to talk about bankruptcy or financial counseling? What's the reason you would want to be on his account anyhow?

I believe if you just add your name and as long as it's in his social security number only you should be fine,,