From what I know is that they still do maintenance on some units there, there is a daily path from Wimbledon Park to Bournemouth depot, and you can regularly see 458's and 455's running to and from the depot. They still store units there overnight, like the 158 for the Lymington branch (as stated on your other thread).
I believe there is also a VEP (3417) in there now for warm storage, kindly provided by SWT.
The Desiro's (444's and 450's) are allocated to Northam depot (Southampton) and are currently having bogie overhauls at Eastleigh, by Siemens. So no Desiro's go to Bournemouth depot unless it is for overnight storage. (That's what I am led to believe anyway)