I think UCSD would give another round of admission. I e-mailed them and they say the review is still on.
Also, I think it depends on how many first round students would decline. lol
Admission decision at ECE department, UCSD is made by committee. I talked to one of my POI, and he is actually in the committee. And he does not think it is even necessary to mention which professor you would love to work with. So I suppose contacting professor might help, but minor. They department offers one year fellowship for the new PhD student. Supported by your POI might help get a RA or TA.
I am still waiting for UCSD as well, but I think my chance is small. I would say sometimes some school even send out offer just before 415.
Good luck for you! Be patience lol