I think that the creature can be considered "the other" in a couple of ways. If we understand "the other" to be "different," it helps in our understanding:
[The Other] has been used in social science to understand the processes by which societies and groups exclude 'Others' whom they want to subordinate or who do not fit into their society.
Indeed, the monster fits such a criteria. Initially, he is rejected by Frankenstein because of his hideous state. The monster is rejected by Victor because he does not fit into his own configuration. When Victor sought to create life and regenerate it, his pursuit was done in accordance to his own subjectivity. Simply put, the monster did not fit this vision. In the exclusion through rejection and the eventual demonizing, the monster represents "the other." Additionally, I would say that Victor's rejection of the monster's pleas to create a companion further reflects "the other" because it shows that Victor refuses to create a social realm whereby the monster can find some level of social acceptance. Victor claims to have realized the folly of his error. While this might be true and valid, his refusal to create a realm of social solidarity and cohesiveness for the monster is one where "the other" is evident, relegated to the outside and never to be reconciled with the self.