For example, you have a token created by Skyline Despot or Lathliss, Dragon Queen, or Utvara Hellkite. Does it activate Sarkhan's Unsealing? I guess the real question is do dragon creature tokens count as dragons?
Relevant text on Sarkhan's Unsealing:
Whenever you cast a creature spell with power 4, 5, or 6, Sarkhan's Unsealing deals 4 damage to any target.
Whenever you cast a creature spell with power 7 or greater, Sarkhan's Unsealing deals 4 damage to each opponent and each creature and planeswalker they control.
- Sarkhan's Unsealing doesn't look for dragons. Any creature spell with power 4, 5 or 6 works.
- Sarkhan's Unsealing requires you to cast the spell. Tokens aren't usually cast. For example Skyline Despot says "create a 5/5 red Dragon creature token with flying". That creates the token, but doesn't cast it; that creature token cannot be countered by a Counterspell effect.
So no: these dragon creature tokens entering the battlefield do not trigger Sarkhan's Unsealing.
You ask another question, "do dragon creature tokens count as dragons?" This is a different question and has nothing to do with Sarkhan's Unsealing. The answer here is yes, and something with e.g. Protection from Dragons will be unblockable (and take no damage if blocking) from these tokens. That's because the dragon tokens are dragons. For example the text on Skyline Despot says "a 5/5 red Dragon creature token" - which means the token is red, is 5/5, and is a dragon; all effects that affect dragons will also affect them.
No, token-creation effects like the ones you named do not trigger Sarkhan's Unsealing. (You said "activate", but the technical term is "trigger")
Sarkhan's Unsealing triggers when you cast a creature spell. In almost all cases, casting a spell starts by taking a real physical card (most likely one in your hand but potentially in exile or in your graveyard if the card allows itself to be cast that way), moving it to the stack, and taking some other specific actions that together form the process of casting.
601.2. To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. Casting a spell includes proposal of the spell (rules 601.2a–d) and determination and payment of costs (rules 601.2f–h). To cast a spell, a player follows the steps listed below, in order.
When a token is created, those are not the steps you follow. For starters, there's no card. And tokens don't exist outside of the battlefield; you can't have a token in your hand, in exile, or in the graveyard. So you can't follow even the first step required to cast a spell, i.e. moving a card from one of those zones to the stack.
Incidentally, the tokens created by these effects do count as dragons, just the same as a dragon creature card on the battlefield would. But that's irrelevant to how Sarkhan's Unsealing works. As I explained above, Sarkhan's Unsealing deals with spells, i.e. things that are on the stack, not with things on the battlefield (like tokens). Plus, Sarkhan's Unsealing doesn't care whether a creature spell is a dragon or not; it only cares about its power.