We never used any official “dual enrollment” program, as dd was too young - only 10. She got personal exceptions from the colleges after interviewing with their VPs of Student Affairs. I arranged the interviews but she brought her drawing portfolio and a box full of sculptures to the VPs, said she would like to take college art classes and will do well. And they gave her the registration.
College courses she has taken will not be used as high school graduation requirement. Private colleges say that they will give evaluations after the admission.
I have personally heard from other parents that their students were generally given 30 semester units credits and were allowed the remaining still be used to meet prereq and requirements. Because engineering / science majors often needs more than minimum graduation units to meet their math / physics /engineering chains, this often had effect of given credits of a lot more than 30 units. Then again it is just a few personal experiences and that’s all.
Regarding general education, I might have been mistaken.
In-state pubic schools, such as University of California campuses have been a lot more generous in giving credits taken at California community colleges, provided that those credits were not used for high school graduation requirements.
Let me share emails that I have exchanged with Stanford admissions;
Note that Stanford uses quarter system, hence 45 units instead of 30.