I am not sure if it is allowed officially, but it is listed in the virtual currencies section. I would be more worried about charge-backs, as most people on eBay use PayPal. It has long been known that it is very risky to sell BTC for PayPal as it often gets charged back with no questions asked, while your BTC is per design non-refundable.
This is really a serious problem. No selling protection in such cases. I have heard of cases of a chargeback for virtual trades on ebay.