The Dalvik JIT compiler focuses on critical sections of code. There's a reason you don't see Hotspot on battery powered devices.
Hotspot get its name from the term of art for a critical section of code, though. That's not something that makes them different from each other; it's what they have in common.
What separates them must be that only one of them was designed with a power budget in mind.
Only in a very general sense. Dalvik's JIT really tries to minimize JIT compilation. Modern Java JIT compilers are oriented around the goal of extracting maximum performance from compiled code. That's priority #1, and there is no #2.
Hotspot get its name from the term of art for a critical section of code, though. That's not something that makes them different from each other; it's what they have in common.
What separates them must be that only one of them was designed with a power budget in mind.