Yes, Lt. Commander A.R.H Nye had earlier been Senior Officer of MGB 312, but in November 1944 was made Senior Officer of a reformed 52nd MTB Flotilla which comprised MGBs 511-518 which were Camper & Nicholson boats originally ordered as gunboats but completed as motor torpedo boats, and new Fairmile ‘D’ boats, 758, 762, 764, 791, 798 and 5020.
I have found other crew members of 611 amongst the membership of the former Coastal Forces Veterans Association, who have written in detail about the boat’s participation in an action off Dieppe in which the vessel was badly damaged, and will get the materials digitised and posted online for you later. This incident however speaks of MGB rather than MTB 611, and happened in March 1944, before your Uncle would have joined, and he may have been a replacement for someone who was injured.
Addendum: Sorry, he joined in 1943 so he would have been present during this time, and may have been a replacement for Able Seaman Norman Black, who died on 28 July 1943