Is it ethical for a firm to pay Uber to provide transportation for clients

Over at My Shingle (a blog I recommend, by the way), Carolyn Elefant discusses whether it is ethical for a law firm to pay a client's transportation costs via Uber.  Does paying for a taxi (or a rental car) for a client constitute a violation of the rule that bars attorneys from providing financial assistance to clients?  (This is assuming the client is involved in litigation because the rule does not apply if the attorney-client relationship relates to transactional matters.)  If so, why would using Uber be different?   Carolyn argues Uber is different.  You can read her comment here.