Yes, they codeshare with SAA. If you do a dummy booking on the VS website to Cape Town it will show the option of a VS numbered flight on SAA metal direct to/from CPT as well as to JNB with an onward connection
Yup I had the travel team at work check out BA - hwoever they have limited availability ont he CPT to LHR route on the day we need to travel, and then only Economy is available. So we've decided to stick with Virgin but travel to/from JNB both hops.
They told me they are still filling seats from people stranded due to the vocanic ash, so seats are at a premium still.