[Bazza6]

Forget your sentences for a moment. You need to go back to basics.
A gerund is a noun formed from a verb. But it acts and functions as a noun, never as a verb. You are confusing the use of a gerund where its function as a noun is emphasised:
"The building on the corner of Elm and Ash Streets was demolished."

and where its origin…origin, not function…origin as a verb is emphasised:
"The building of new highways is our top priority."

You write:
"I have learned that BE USED TO must be followed by a noun of a verb in its gerund form." I presume you meant to write: "...by a noun OR a verb in its gerund form…"
Of a gerund, that is like saying of a man: this is 44 year old Paul, a boy in his man's body.
It doesn't make sense.

In your sentences:
1) I'm used to dominican food (Noun)
1a) I'm used to eating dominican food. (Verb)
(1) is a shortened form of (1a)! Take out 'used to' and you get:
1a. I am eating dominican food
Do that with (1) and you get:
I am dominican food (!!!)
(1) "I am used to dominican food" is shortened from "I am used to eating dominican food."
And what is implicit is the full sentence:
I am used to the eating of dominican food.