Combining parts from a MacBook Pro with a Dell Inspiron
Technically speaking, yes the CPU would work (provided it was still functional). Apple makes no changes to the (Intel) CPU making it "Mac only."

However, (and this is a big one), where Dell typically uses a socket, Apple solders the CPU to the board - you can remove the Dell CPU, but you need to de-solder it from the Mac.




What you would spend on the labor just to remove the CPU is far more costly than surfing eBay for a deal on a compatible CPU.