Back to the question at hand, I'm assuming one would only get an online CPR certification to fulfill some sort of job requirement, and therein lies the rub: Online CPR certification is as valid as an employer says it is. If your job accepts an online CPR certification, it counts. If not, it doesn't.
If you want to be a doctor, you have to get your training at an accredited medical school and pass the boards. Want to be a nurse, an EMT or a paramedic? Similar process. There are laws in all 50 states defining what it means to be licensed to do any of these professions. The dirty little secret of CPR and first aid training is that nobody's watching.
CPR certifications are completely unregulated. Whether you take a course online or print the card on your home computer without ever paying a cent doesn't matter. There isn't any national CPR accreditation process to vouch for the legitimacy of any organization. That's true of the Red Cross, the American Heart Association, or Jerry's CPR and Muffler Shop.
What makes Jerry and the American Heart Association different is their motivation. Jerry is in it for the money. He's being an entrepreneur, identifying a hole in the market and filling it. What Jerry sees is that you need CPR certification and figures he can fill that need in a way that satisfies you and your employer. Whether or not you actually learn CPR doesn't matter to Jerry.
The American Heart Association, however, wants to teach you a life-saving skill and promote saving lives. They spend time and money trying to figure out the best way to motivate you to learn and then to teach you in a way that you retain the information for as long as possible. The American Heart Association also wants CPR to be as effective as possible, which means studying the procedure and constantly refining it to be a better tool for saving lives.
So Jerry runs a web site from the back of his Muffler shop and makes a lot of money but doesn't teach anyone how to do CPR, while the American Heart Association sponsors lots of community classes around the country, teaching lots of folks how to do CPR, and doesn't make any money. Which certification do you think is going to better represent your ability to do CPR?
I like convenience as much as the next guy, but if I've decided my business needs people trained in CPR, I'm not going to accept Jerry's online CPR certification. I'll tell my folks I'll only accept a card from an organization I trust. As a teacher, I limited my students to Red Cross or American Heart Association CPR certifications. I know those organizations take training -- and trainer oversight -- seriously.
The old saying cautions you not to "just go through the motions." Online CPR classes don't even let you do that. Take a CPR certification course from a trusted organization and walk away confident that you can save a life.