If a celebrity willingly agreed to allow me to video him saying my business slogan can I be sued if video is used to promote my business?

Those celebrities control their right of publicity and if you use the video in the way you state, you are implying their endorsement of your business. To use it legally in this way, you would need to have a written agreement that specifically states how it will be used. If not, they can sue you for breaching their right of publicity, for damaging their reputations, and possibly for other things. It sounds like you actually tricked them, because they did not realize that what they were saying is business slogan. Tricking people is not good. Most professional athletes cannot endorse a product without their agent and lawyer carefully considering if this is a good move for them, career-wise and financially. It's worth asking, though.

You need to have permission from the celebrity to use their video image to promote your business. That permission can be videotaped permission where you specifically ask them on camera if you can use their image to promote your business and they respond with a yes. Or that permission can be written permission that they actually signed. But without such clear permission in one of these two forms, you can not use the video you got. Permission for commercial use as you want to do must be clear or usage is not permitted.

You would need a person's release or contract in order to use their name, image, or trademark.