I just sent an email to one of the group leaders stating I would like to do research for a thesis there.

There is no formal interview or hiring process if you a grad student at UC Berkeley and your scientific adviser has a shared employment with UC Berkeley and the lab. It is often up to your adviser and the funding sources to put you on a campus or LBNL payroll. There is no differences in salaries. The salary information for this position is public and the salaries at LBNL for graduate student researchers are matched to the salaries of corresponding departments on campus.