The 1830 typesetter omitted the as, either by accident or because he thought it sounded better without the as. There are two cases that support the lack of as:
Nonetheless, there is one example where consider is used with as:
Thus either usage, with or without as, is possible. The critical text will therefore follow the earliest textual sources in determining whether as occurs with “to consider X (as) Y”. Here in Mosiah 3:9, the as will be restored.
Summary: Restore in Mosiah 3:9 the as in “they shall consider him as a man”, the reading of the printer’s manuscript (here the earliest extant source).