can i play ojama trio and activate s.polymerization to bring ojama knight?

I believe so...

couldn't you also bring out Ojama King?

the text of king states ojamagreen+yellow+black.
knight text states 2 ojama monsters.

Super Polymerization: "Discard 1 card. Send, from either side of the field to the Graveyard, Fusion Material Monsters that are listed on a Fusion Monster Card, and Special Summon that Monster from your Fusion Deck. (This Special Summon is treated as a Fusion Summon.) Spells, Traps and Effect Monsters' effects cannot be activated in response to this card's activation."

Notice the bold section.. to the graveyard. Token monsters cannot be sent to the graveyard, so it is not possible to use them in a fusion summon.

Thats wrong!

If you can use this combo, then you use the above combo.

Dragon (on field/in hand) + Scapegoat +DNA Surgery + Polymerization

Have been told this works, so why cant the above combo work.

That's because the Ojama Trio + Super Polymerization combo DOES work. Any and all Fusion- and Ritual-summoning effects do not send/tribute the monsters as a cost. It is part of the effect resolving, and thus why it is legal to activate Super Polymerization/Future Fusion/etc. while Macro Cosmos is active. And because of this, it is legal to use tokens as well.