There is no language calling out Racial as a bonus type specifically (like for Trait bonus in the Advanced Players Guide).
It is not on the chart from Ultimate Magic for designing spells.
Only the paragraph above lets us know it is a bonus type.
There is a section in the rules that specifically calls it out as a bonus type AND states that racial bonuses stack with other racial bonuses.
I'll see if I can dig it up.
EDIT: Found it.
Bonus Types: Usually, a bonus has a type that indicates how the spell grants the bonus. The important aspect of bonus types is that two bonuses of the same type don't generally stack. With the exception of dodge bonuses, most circumstance bonuses, and racial bonuses, only the better bonus of a given type works (see Combining Magical Effects). The same principle applies to penalties—a character taking two or more penalties of the same type applies only the worst one, although most penalties have no type and thus always stack. Bonuses without a type always stack, unless they are from the same source.