Radar vectors when VFR (or SVFR) are dodgy, as complying with the vector might put you IMC. Don't forget also that SVFR exempts you from the IFR height restrictions (Rule 21, I think it is, but not Rule 5) and if you are being radar vectored you must be at or above the relevant MSA in the Radar Vectoring Area. Most ATCOs would I think steer clear of offering R/Vs to VFR/SVFR for this reason, whether day or night. You would be daft to accept them as well, as it might put you in a situation you are not qualified to handle.
Class of airspace: Assume we are talking about Class D or Class A. My original comments about responsibility for separation then apply.
Ref the question about ending up 50ft apart: Difficult, but ultimately SVFR is a see and avoid clearance, so it will be the pilot's responsibility if you get that close. If you report not visual with called traffic I would hope ATC would do something before you got that close!!
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"Take-off is optional, Landing is mandatory"