Is Blaze the Cat in SonicX?

No. Blaze the cat never made any appearances in Sonic X or any other Sonic the Hedgehog movies/shows.

She is seen in these games:

Sonic Rush (Playable)

Sonic Rush Adventure (Playable)

Sonic and the Secret Rings (Unlockable, partymode)

Sonic and the Black Knight: She is known as Percival.(Playable)

Sonic Riders: Zero Gravity (Unlockable)

Sonic the Hedgehog 2006 (Playable)

Also she is seen in Super Smash Bros Brawl as a trophy and a sticker.