my question was: can they apply for any US immigration benefits up to USC under the current law ?
Yes. You can look at statistics of natualization by country of birth. America is listed. There was a post before here about those statiscs.
Speculations give three possibilities about those US born naturalized citizens
(1) children of diplomats born in USA
(2) People who are born as US nationals but not US citizens in American Samoa and Swains Islands
(3) Natual born US citizen who renounced US citizenship and later immigrated back into USA
For (1) and (2), they need to immigrate to USA first. Therer is immigration quota by country. I don't know how quota is allocated to
USA.
(2)