Question: If I apply to one UC and get rejected, will other UC's accept me even if I did not apply to them?
It's always nice to get good news when you don't expect it ... kind of like winning the lottery when you never even bought a ticket. ;) But, unfortunately, in this case, you can only be accepted at the UC campus(es) to which you have applied. There is a per-campus application fee ($70 per campus for domestic students; $80 for international students). So, if you want to be considered by multiple schools, you need to pay for it.
If you wish to attend a UC school, you should be sure to apply to campuses with a range of selectivity with the hope that at least one of your choices is "Safe" for you.
If you want to find out how your qualifications mesh with the expectations of the UC schools that interest you and also look for other colleges that might be good fits, try College Confidential's Supermatch. See http://www.collegeconfidential.com/college_search/