Before, during or after the referendum?
Montenegro only achieved independence by a margin of 2,300 votes. There was speculation that they were Muslim Albanians shipped in to swing the vote in favor of independence, but it was an unproven allegation.
Here's Wikipedia's posted ethnic composition, which may or may not be completely reliable. Note: Listed Serbs and Montenegrins are interchangeable, but those wishing to continue the union often called themselves Serbs and those wishing independence called themselves Montenegrins. The listed Bosniaks are Muslims as are most if not all of the Albanians:
Ethnic composition according to the 2003 census:
Montenegrins: 267,669 (43.16%)
Serbs: 198,414 (31.99%)
Bosniaks: 48,184 (7.77%)
Albanians: 31,163 (5.03%)
Slavic Muslims: 24,625 (3.97%)
Croats: 6,811 (1.1%)
Roma , Egyptians & Ashkalis: 2,826 (0.46%)
http://en.wikipedia.org/wiki/Montenegro