No wild pokemon hold the Dusk Stone as an item however you can obtain Dusk Stone from the Secret Super Training Watch Out! That's One Tricky Second Half.
Houndour can be obtained by trading from Pokemon X or Y. It cannot be caught in the wild in Pokemon Omega Ruby and Alpha Sapphire.
There is no roller skate item in Alpha Sapphire.
You can catch Skitty in Pokemon Omega Ruby and Alpha Sapphire in the barks of trees.
You battle Kyogre for your chance to capture it in Pokemon Alpha Sapphire after you capture the groudon.
Magikarp
Yes, Tm's in Pokemon Omega Ruby and Alpha Sapphire are re-useable
No, you will need to trade for them or transfer them via Pokemon Bank to get them in Pokemon Omega Ruby and Alpha Sapphire.
The Prism Scale cannot be obtained in Pokemon Omega Ruby and Alpha Sapphire. You'll need to trade for a Pokemon holding the Prism Scale to get it.
You will need to trade for Weedle or breed Kakuna. Kakuna can be found only in the Safari Zone in Pokemon Alpha Sapphire and Omega Ruby.
No
It is not yet known if there is a building location for the GTS in Pokemon Omega Ruby and Alpha Sapphire.
Yes, all the TMs that were in Pokemon X and Y will be available as TMs in Pokemon Omega Ruby and Alpha Sapphire.