I suspect the conditions were pretty much as safe as they are for a dark rig departure with no visual references - when, as has been discussed before, the crew climb vertically on instruments before pitching down to generate translation lift to achieve VMini and climb away
I would hope that all rig departures are very much with visual references until the rotation point - at which point the transition to instruments occurs. Vmini doesn't figure much, normally Vtoss and Vy are the pertinent speed to note.
By far the best way of doing so is to achieve VMini+ in VMC then climb into IMC on instruments at VMini+ to MSA
Why? Surely you would aim to achieve at least Vy, rather than waffling around for a few thousand feet at 40-50kts with a lower climb rate?