The question is who owns the copyright in the video. Chances are the waitresses signed releases when the yagreed to appear, but the videographer, the venue, the contest host (most likely) all may own the copyright in the video so publishing it in any format (commercial use or otherwise unless it meets fair use exception which your use does not) would constititute copyright infringement.
The answers given are informational only and do not constitute legal advice. Please feel free to contact me if you want to obtain legal advice from me.
Even if you are the copyright owner of the video (by having filmed it), unless you have written consent, those that appear on the video have a publicity/privacy right that they can enforce and could have a case against you to a.) force you to remove the video; b.) stop you from posting it or playing it in public; and c.) seek damages. This publicity/privacy right is a state-based right, not federal. However, because of the Internet, the determination of proper venue/court is more gray and someone could potentially forum shop for the state with the strongest privacy laws. Additionally the location may have a claim against you if they did not sign a location release and any registered trademarks that apears in the video (ie: Beer brand, etc.) may have a case against as well. What is the likelihood that someone will file one of these? Who knows... Consult with an entertainment attorney who can gather more facts and give you a legal opinion.
The rights of privacy and publicity of the contests is likely, by agreement, now owned by the owners of the contest, so it is likely not the contestants but the promoter of the contest whose approval you need and don't have. The posting of it on YouTube is likely a relatively low risk proposition unless this is a major event like Miss USA, Miss America, or Miss Universe, as the contest promoters of other swim contests likely crave publicity and likely will not object. On the big contests, however, they already are known as well as they can be and now are making revenue by maintaining a stranglehold on the publicity rights and brand names, both of which you would be likely infringinging. So figure your right is proportionate to the notoriety of the contest. If it is the Miss Roanoke contest almost no risk provided you are not doing crotch shots or boob shots or other soft porn.
So far, this is free to you. Until you pay a fee, I am not your lawyer and you are not my client, so you take any free advice at your sole risk. I am licensed in IL, MO, TX and am a Reg. Pat. Atty. so advice in any other jurisdiction is general advice and should be confirmed with an attorney licensed in that jurisdiction.