S.R.
I just wanted to say good for you in being pro-active in soliciting advice of others on this issue. I would so much rather have my children in your daycare than in one with a provider such as the one who commented that they don't have the patience to deal with potty training. Sounds like that individual is in the wrong field. When she says that parents don't pay her enough money to potty train their kids, wow!! Sounds like they're already paying her WAY TOO MUCH given her lousy attitued, which most certainly translates into sub-par childcare. Working parents have a tough time potty training in general and I can't imagine my daycare provider not being willing to work with me on the issue or even unwilling to work on potty training period!
I can tell that you, however, are a true childcare professional who actually cares about children and understands the needs of the families that you serve. I think having a basic policy is great and I also think you should be flexible so that the training can work out best for all involved. Also, keep in mind that many first time parents actually look to the daycare provider for advice and instruction and would likely appreciate any input from you.
For us, going cold turkey on underwear was the only thing that helped move the process along, but we have had many, many accidents. At my daughter's daycare center (2 year old class) they had carpeting that was very easy to clean since a class of 10 potty-training kids was a messy proposition. When we lived in the city, my daughter went to a home daycare where the provider had owned her daycare for over 20 years. She had a rule of "no pullups," but my daughter was little then, so I never really discussed her reason for the policy.