I recently contacted a national chain that sells the dried corn as suitable for rabbits and got the following response. Not totally sure what to think, but even if the digestion bit is true, there's still too much sugar in it, and just cos most commercial rabbit treats have corn in doesn't mean I'd ever feed them to mine...
" am writing with regards to our recent email communication regarding your concerns about the Corn on the cob animal treat.
As advised I passed the information onto our Quality Assurance department and our supplier has provided us with the following information:
It’s correct that the hull of corn kernels is composed of very tough polysaccharides (cellulose, hemicelluloses A, B, and C) and lignin. To humans these are classed as indigestible in that the human digestive system cannot break them down to extract nutrients (sugars). However rabbits (and other ruminants like cattle and horses) have a very specialised digestive systems that includes gut flora that can partially breakdown and extract nutrients from cellulose and hemicelluloses. However whilst not all of these fibres are digested completely they, with the lignin, are very important to the health of the rabbit giving the same benefits to the rabbit’s health as dietary fibre does to humans. So rabbits need both digestible and non-digestible fibre (like the lignin) in their diet. So much so that both pet and wild rabbits benefit from eating the bark and heartwood or certain trees (both a rich source of digestible and non-digestible fibre) despite the fact they cannot full digest them in the same way they cannot with the whole corn kernels.
The issue with the corn and digestion/blockages it more to do with if it’s dried or fresh. Due to the shape of their head and position of their eyes rabbits cannot ‘see’ the food they eat. They also cannot vomit (the standard way for most animals to expel unsuitable food) so they ‘feel’ the food with their lips and then bite into it using their incisors and then pre-digest it by grinding it with their molars. So the hulls are also less of a problem with dried corn, as a rabbit will almost always grind the kernels into very small bits before swallowing. But fresh corn is another matter. The endosperm is soft, and the hull is pliable, so the whole kernel can be swallowed with little chewing (especially in larger breeds). If a lot of hulls are swallowed whole, they can potentially result in intestinal impaction. However even with this the risk can depend on other factors. For example impaction can also be caused by the rabbit’s own fur and even some tough hays. Rabbits ingest fur when grooming and some even chew and eat fur, especially if they are not eating enough hay. In fact it’s the eating of hay with its indigestible fibre that helps keep the rabbit’s gut motile which then helps to prevent hairball blockages. Rabbits that receive little exercise also have reduced gut motility, so the combination of feeding fresh whole cobs (or ingesting hair), a lack of good hay and limited exercise tend, together, to result in most cases of intestinal blockage.
I’ve known a lot of people who feed their rabbits fresh corn cobs with no problems suggesting that other factors need to play apart.
The key thing to stress with corn cobs is that they are marketed only as treats. We/you even put a responsible warming on the packaging: This is a complementary pet food. Remember that just like us, your pets can have too much of a good thing, so we recommend feeding one cob every 1-2 weeks to your furry friend.
It’s also the case that 90% of rabbit treats use corn or other cereals as their main ingredients, so if corn cobs couldn’t be sold for rabbits from this point of view then most retailers would need to take almost all their treats of their shelves apart from a lot of our ‘Naturals’ range which are cereal-free. Often these other cereal treats are made from processed cereals which make the starch more biologically available and have less fibre and vitamins/minerals, so are arguably worse still.
At least dried corn cobs also make them work for their treat: so they cannot eat lots of corn quickly (in fact often very little gets actually eaten), it helps to alleviate boredom and helps to wear growing teeth.
I do hope you find the above information helpful.
Thank you once again for contacting us."
We even put some to dry for the winter, but it occured to me that maybe it's not good for them. It's not the first time or year (she's 4) since we give it to her and she hasn't had problems, but still, I'm worried. 
