Can I dismember any arm, leg or head in "Aikido with sambo"?

Yes, but it requires a lot more force than in Judo, for example.
Usually you will end up with a fracture, but if you time something right or just get lucky, you will get a dismemberment.

The dismemberthreshold is a lot higher in Aikido than in most mods. The fracturethreshold is lower than the dismemberthreshold, that's why you get fractured easier than dismembered. The good thing with Aikido and Sambo is that you can't rely on your opener (as in Judo). You have to rely on your position and available joints. Aikido/Sambo takes more skill than Judo or Kickbox.