Threshold Signatures for RSA and DSA
Regarding your first question, it is my understanding that DKG techniques are in practice mainly used for offline signing, such as when a certificate authority issues new intermediate CA certificates. Using DKG for online signing, such as server side SSL/TLS, is not a problem that is solved by the papers you refer to, since the threat scenario is significantly different from that of offline signing. More precisely, to guard yourself against unauthentic signing requests in the online case, the front end server has to authenticate itself to the back end key share servers, but if it is able to do that, it is able to store a private (or secret) key securely and doesn't really need DKG in the first place.