there is no issue with HTTPS and Webservice Datastore, in one particular version of DS 12.2, it was not working if the DS Servers were behind a proxy which was fixed in subsequent patch
you are on DS 4.2, there should be no problem using webservice datastore
please refer to following link and other posts in that forum to trouble shoot the DS WS issues with HTTPS/WS-Security etc
Help with batch job to web service (https)
if you still have problem please open a OSS Message and I will take a look, if you already one open, let me know the number