Given the context (a song in Portuguese sung by a Brazilian group), I would assume that when written
conmigo it's indeed a Spanish version of the song; and when written
comigo is a Portuguese (original) version of the song (keeping in mind, of course, that
baila is written in the same way in Spanish and in Portuguese).
Although, here's a fun fact regarding the use of
comigo is a word that does exist in Spanish, although it's quite old and is no longer used.
The Diccionario de la Lengua Española has an entry for
1. pron. person. 1.ª pers. m. y f. sing. desus. conmigo.
As you may notice, the Dictionary states that it's a word that's no longer used. Even in a dictionary from 1729 (Autoridades), the entry states that the word is antiquated:
Comigo: adv. Lo mismo que Conmigo. Es voz antiquada [...].