What is the difference between Sushupti and Samadhi with respect to the state of the mind?Would it be correct to say that the intellect or buddhi is active in Samadhi and dormant in Sushupti?
Yes.
Chitta will be active in samadhi; (That is why one can remember the experience of being in samadhi, later)
Ahankara (and chitta) will be active in sushupti (So that one can say that 'I' had a good sleep, later)
Buddhi is the decisiveness faculty- predominant only in jagrat avasta.