Legal question regarding rippling balances between Ripple gateways
In the U.S., FinCEN has specific rules regarding money transmitter laws for those providing money services.  Users who simply patronize a money service are almost never considered money transmitters or providers of a money service.  So, in your example, the answer is likely to be no -- no, a withdrawal from one service and a deposit to another would not likely cause you to need to report the transaction to the government. 

As far as taxes, that too is jurisdiction-specific.  In the U.S., capital gains taxes may apply however in your example there was no gain so there would then likely be no need to report the transaction on the tax forms.

Disclosure: I am not a tax advisor.