<<Disclaimer: Verify this information before applying it to your situation.>>

The consensus seems to be that the "bran" in the recipe is rice bran.
Someone sent me some interesting facts on gf bran:

Two g.f. brans are available from corn & rice.  Probably was rice bran.  Now
since they have developed a process to remove the oil (which made it go
rancid quickly), it's being used more.  It's a water soluble fiber, like oat
bran (not g.f.), may be even more healthy than oat bran from a 'hear healthy"
point of view.  Now products markets rice bran in the Midwest.  Store in the
freezer to keep it fresh longer.  Give it the "sniff test" before using.  If
it's rancid, you can tell.

Thank you everyone, I'm looking foward to trying the raisen bran muffins (for
those that didn't get the first post, look on webmd.com).