RTTYSkimmer and SDR-Bridge setup questions

You can of course but only as a 'secondary connection' in Aggregator parlance. This is due to Aggregator requiring CW Skimmer compatibility. So SDC does work but only if CWS is also connected which defeats the object since, if you have to have CWS, then SDC though a better Skimmer is somewhat superfluous. You also have to be rather careful how you set up SDC Skimmer since it uses an alias by default which is not acceptable to RBN. That can be overcome but overall you might as well just use CWS if you run Aggregator. I have not raised this subject with Yuri, he might be able to provide more information to anyone who asks him, but I feel fairly certain his intention for SDC is to take Spots from but not give Spots to RBN.