Descent 2nd Edition Community Rules Reference Guide
Rule book page 26, first sentence under heading "Summon".
Some abilities summon other ally figures to the board.
Emphasis by me.
Rule book page 18, under heading "Character Turn".
An ally is any figure that fights with a character. This term includes summoned figures, but does not include the character itself.
Thus, all characters and summons are allies. All monsters are allies.