There are a very limited number of ships allowed in Glacier Bay for environmental protection purposes. You may want to check other cruise lines or look at Hubbard Glacier or some other such alternative.
The two times we have been in Glacier Bay, out ship was the only ship within the bay during that time period. There may have been another at different hours but that I do not know.
The two times we went to Glacier Bay were both on Holland America ships, The Westerdam and The Amsterdam.