Yes, you can hatch bantam eggs under a LF hen. You can actually put more eggs than standard size eggs under her - I would say between 10-12... maybe a few more depending on the size of the hen.
My LF hens smashed some of my banty eggs, when they would get in and out of the nest to eat. I ended up removing the last 3 out of 7 when I picked on up and it was bleeding all over my hand due to smashing, 2 of the 3 hatched in bator.