<p>Is it OK if the same OpenSSL context is used by several different accepting sockets?</p>

<p>In particular I'm using the same boost::asio::ssl::context with 2 different listening sockets.  </p>

Yep, SSL_CTX--which I believe is the underlying data structure--is just a global data structure used by your program. From ssl(3):
SSL_CTX (SSL Context)
That's the global context structure which is created by a server or client once per program life-time and which holds mainly default values for the SSL structures which are later created for the connections.