You can. But you can't erase their internal program memories, you'll have to use the salvaged 8051's with external program EPROMs, for which you will have to sacrifice their P0 and P2 ports. See any 8052 family member's data sheet on how to connect the EPROM.
A new 8052 may cost you less money than a salvaged 8051 costs you trouble though. Only recycle them if it's a hobby.