I think it's interesting that when reading through the OT, it often appears to imply that other gods exist, or at least might exist. For example, you have constant commands to the Israelites along the lines of "you will worship no other gods before me," which seems to imply that there might indeed be other gods, but they aren't to be worshiped. There are also descriptions of the israelites getting into trouble for worshiping other gods, and it's never actually stated that these gods don't exist, that the israelites are foolishly worshiping nothing - merely that the isrealites were sinning by worshiping them.
In Exodus 15:11 it asks "Lord, who else is like you among the gods?" and then goes on to explain how nice Jehovah is. A plain reading of this would seem to be that the author is acknowledging that other gods exist, and praising Jehova as better than them. There are also various places where Jehovah is referred to as a "god of gods," which might be meant to be taken as metaphor or something, but again a plain reading of the text would take this to mean that other gods exist, but aren't as powerful as Jehovah.
Interestingly, the command "you will worship no other gods before me," literally doesn't even seem to forbid the israelites from worshiping other gods, so long as they put their loyalty to Jehovah first.