My friend was just on the Magic with her 3.5 year old who isn't potty trained and he could only attend Oceaneers club with an adult during open play. They were absolutely adamant that if he wasn't potty trained, he couldn't remain in the club. Same with pull-ups, they told her that unless it was during open play and she was there to assist him if he needed the bathroom or his pull-up changing, he couldn't wear one. And parents were allowed into the bathroom. No CMs.
My DD is almost 6 and has cerebral palsy. We are still in nappies/diapers. She also could not attend Oceaneers. Not in 2011, last year or later on this year. When you register them for the club it asks you whether they are potty trained or not.
It sounds like your friend had a bad experience which is unfortunate. Perhaps the cast member she spoke with wasn't aware that the child in question was over 3. It is a discrimination issue to turn away a child between the ages of 3-12 due to potty training reasons at the Oceaneers Club / Lab. If you look at the
DCL site they have removed all language related to potty training being required in the club. DCL would be risking a lawsuit. If this happens again or if the OP runs into this type of issue I would absolutely ask to speak with the club manager.
This is the information on the DCL website regarding Children with Special Needs
Children ages 3 to 12 with special needs are welcome at Disney's Oceaneer Club. While we cannot offer one-on-one care for your child, simply let our counselors know in advance and we will accommodate the best we can. If your daughter does not require one on one attention and would be comfortable in the club on her own I don't see that the diaper situation would be the reason she could not be there on her own. They even offer pagers (in addition to the wave phones) if they need to get ahold of you quickly. If you need to be with your daughter during open houses I'm sure the time spent is very special to you both.

Hoping that you and your family have wonderful cruise in a few months.
In my previous post I mentioned the cast member who works on the ship in the clubs. He has been answering any/all questions. I know we've all read that agents don't always know the facts. This person actually works in the clubs so his responses are first hand. This is a quote from the first post on the thread. The same response has been repeated multiple times as parents ask the question.
http://www.disboards.com/showthread.php?t=3186484&page=66
My child is under 3, can they go to the Oceaneer Club or Lab?
Not unless they fulfill the following requirements:
-Are fully potty trained (can use a toilet and undress themselves independently, must not wear diapers or pull-ups.)
-Are capable of speaking and communicating their needs to an adult who is not in their family
-Are independent (i.e.: will not spend the entire time in the space crying and waiting by the front gate due to separation anxiety)
-Are well socialized and do not demonstrate any fear of Counselors and will be able to follow instructions.
-Are generally within 2 months of turning 3 years old.
This is the general guideline we follow when approving children under the age requirement into the space - which might seem like a tall order for toddlers, but there are indeed tons of 2-year olds who possess all of these qualities and have matured and grown quite rapidly! So don't fret if your 2-year old doesn't quite match up, kids mature at different rates. If a Counselor is ever in doubt about the eligibility of an under-3 into the space, they will ask for a Manager to come speak with the family and have a look at the child.
My child is over the age of 3 and is not fully potty-trained, can they still go into the space?
We are required to accept any child between 3- 12, regardless of whether they are potty trained. Once they fall within our age group, you may have them in diapers and pullups (we have had many cases of children with bowel issues, or late potty-training, or developmental delays needing this!). We will ask you to check on them frequently as we aren't allowed to change them ourselves.