gamefreak says no.
torchic could've been fire/flying (a chicken), but it becomes a street fighter instead.
piplup could've been water/ice (a penguin), but it becomes an fatass steel penguin instead.
I doubt that by being an otter Mijumaru would gain ground as its second typing just because it makes more sense.
Nintendo says no.
That's because of Blaziken :P
That's because of there being a rather large number of water/ice types already :P
Otters live by lakes and ground is simply a better typing for it to have than either ice or steel. Just too many weaknesses and not enough strengths with those typings.