Cullimore was making approximately half of Samsonov's contract, and when you buy out a player's contract, the salary cap hit is spread out over twice the length of the contract. In this case, since Cullimore had 1 year remaining, his 1.3 million contract will count $650k each this year and next. The Habs had intended to do the same to Samsonov, but would've been about a $1.75 million cap hit for each of the two years. Habs gain $1.1 million in cap space.
Salmaleinen's one of those guys that scored in Europe, but hasn't had much success here yet. He's a restricted free agent, so I imagine whether or not the Habs keep him will depend on how much money he asks for. He could fill in as a 3rd/4th liner, but probably not much more. Like Koivu, and recent addition Janne Lahti, he's of Finnish descent.