I've just made dumplings using butter as I'd ran out of suet, looked it up on net and found you could just substitute butter/marge for suet as long as it's half the weight of the flour (self raising and had in oven for 30 mins)
They looked ok, not 'cloud' fluffy or as big as suet ones and were a definite shade of yellow! The did taste buttery, they were still fluffy inside but I admit the taste didn't seem 'right' to me - like as if I'd added mint (I'd only added a bit salt, pepper and parsley)? Asked DH and he agreed he preferred the suet dumplings.
Am wondering if it would be the same made with lard/part lard? Or would that be revolting?