I know the post is a month old, but Uncle Mike does indeed have a last name -- it's Mike Lane.
Presumably he's Sam's brother.
From the "Church of Metropolis" script:
LOIS & CLARK
The New Adventures of Superman
"Church of Metropolis"
TEASER
FADE IN:
1 EXT. AMERICANA CAFE METROPOLIS SOUTHSIDE DAY #1 1
A charming bistro, empty but for LOIS and CLARK sitting at
an outdoor table, amid the remains of an enormous meal.
Lois' UNCLE MIKE LANE, a hearty ex Marine, comes out of the
restaurant brandishing two massive slabs of cake.
That's not to say that you couldn't give Ellen a brother named Mike, too, but the Uncle Mike from the show is a Lane.
Kathy
