Yes, it is fine under the current system (and prior version, too). They currently have no way to police it, so it has to be okay even if they would like to eliminate it. But the arguments are all over the place. On one hand it's argued that riding B while waiting for A is fine and within the rules. On the other, it is claimed to be an infrequent thing. Yet when the subject of eliminating that privilege comes up, people get defensive. If it is used so infrequently as some would like to claim, why care about it being taken away? Also, it is one of the big things that makes lying to get DAS so appealing. It makes for a free and superior product compared to G+. If Disney is going to go through the trouble and expense of doubling the number of tapstiles at every attraction to accommodate what you deem "fair" for AQR, you can bet they're going to get their money's worth and eventually eliminate the ability to ride something else while waiting for a DAS return time.