When the pitch accent is on the first mora, i.e., the type 1, もえる refers to 萌える, meaning "to sprout", not 燃える(= type 0/flat). Similarly, the type 2 /キタ]ゾ/ is 北ぞ (=classical だぞ), not 来たぞ. Thus, /モ]エテ キタ]ゾ/ could be interpreted 萌えて北ぞ as a stand alone sentence without any context.
It's possible to be interpreted 燃えてきたぞ from the context, of course, but it sounds extremely odd.