VS is not in Skyteam yet (unlike AF/KL), so it is not covered by Skyteam rules. You'd get lounge access at US/UK Clubhouses due to same day flights between US and UK. Lounges at other stations are not covered, however, by DL-VS agreement. VS does not grant access to lounges at non-US/UK outstations (like JNB) or shared access third party lounges (if they still had one in DEL) unless you are flying in Upper Class. Having an international flight or same day US-UK flight is not valid for those lounges.