Nothing stops you putting a FIS on a squawk and identifying it (for example to make it 'known traffic') to yourself. If passing tfc info to FIS traffic you could always use the time-honoured phrase 'traffic believed to be you has tfc etc...'
IMHO anything that stops a potential midair happening is fair game (MATS Pt1 sentence 1) - and I'd defend THAT against any desk-bluntie in a court of law.