Sure, that is in fact, one of the justifications for training military pilots in Formation approaches and landings... To lead an aircraft with an emergency down to a safe landing in IMC conditions when their emergency would otherwise prevent them for executing an instrument approach on their own (instrument failure, or electrical failure, etc.).
But just to comply with an ATC instruction to shoot an ILS approach (assuming both aircraft are ILS capable), would not seem appropriate to me.
... and, before someone else points this out, this is an inherently dangerous procedure, which requires a great deal of training and proficiency. It should not be attempted without both.