I might actually give the guys at LOAV a call to find out
OK, I did just that and had an interesting chat with the met guy there. The SC and ST do indeed refer to Stratocumulus and Stratus clouds. Apparently all GA airfields in Austria (those with a met guy) report the clouds in that way. Reason being the mountains which can lead to extreme wx variations of short distances (I can attest to that!). I have not yet tried it, but according to the gentleman I just spoke to, looking up any Austrian GA field in Homebriefing.com will reveal METARs of this type.
Another observation made during the conversation was that LOAV can have the rather unusual wx combination of high winds
and fog. The explanation for that is the vicinity of the Neusiedersee, a large lake to the SE of the field.