My advice would always be to wear a perscription mask instead of contacts, but as with everything if you know the risks the choice is yours. Unfortunately there is always the senario that someone will wear there lenses, dive in them, then sleep in them - and guess what....nothing, they are perfectly ok. Then you get someone that will be utterly complient apart from once and bang "red eye".
The most important issue here is the reduction of risks. It is upto the individual, in consultation with an eye care specialist, to decide when the risks are low enough; Holiday diver, then yearly/monthly lenses with the correct cleaning regime would be fine. semi addicted diver such as myself (40 - 60 dives/year) then i would urge a move to daily wear lenses, more dives than that then I would suggest a move into a perscription mask, not only for safety but also probably for costs. But I would never ever advise anyone that wears continuous wear lenses to dive in them.
HTH
Ian Daly