"Han går som en älg."
Translation:He walks like a moose.
You might be correct when it comes to English, but the Swedish sentence could not mean that.
If you'd want to express that someone dresses up as a moose in Swedish I would suggest;
A) to say "Han klär ut sig till (en) älg" - "He dresses up as a moose" or
B) "Han går som älg" - omitting the "en" in this sentence gives a different touch to it and, knowing the context, I would understand this.
That's only in American English. The species found in Sweden and Finland, Alces alces, is called moose in American English and elk in British English.
The species called elk in American English is called wapitihjort in Swedish and and wapiti in British English.