Your problem is due to the fact that Okami is not Brawl Compatible, and only certain games are .FPK files (Tatsunoko vs. Capcom for example) not all Brawl Files, and Some Compatible games have .Arc format (New Super Mario Bros. Wii for example)
Heres a list of game ISOs that utilize game models that are similar and compatible with Brawl
List of known games with MDL0 files:
(Total: 58 -- 2 unconfirmed)
Animal Crossing: City Folk
- (The models are packed in ARC files and need to be exported with an external program.)
Arc Rise Fantasia
- (The models are compressed and either need to be decompressed using this QuickBMS script, or dumped from Dolphin's memory.)
Arkanoid Plus [WiiWare]
Bomberman (JPN) [Retail] / Bomberman Blast [WiiWare]
- (The models are packed in ARC files and need to be exported with an external program.)
Bleach: Versus Crusade
- (Models are almost the right size. They need to be scaled 1.3x-1.55x their original size.)
Bubble Bobble Plus [WiiWare]
- (Files are compressed strangely and need to be extracted using a memory dump from Dolphin.)
Captain Rainbow
Case Closed: The Mirapolis Investigation
Castlevania Judgment
- (Models are small and need to be scaled to 11x [?] their original size.)
Cooking Mama
Dead Rising: Chop 'Till You Drop
Dewey's Adventure
- (The models are packed in ARC files and need to be exported with an external program.)
Dragon Ball: Revenge of King Piccolo
- (The models all have generic filenames, and are packed in uncompressed *.BIN files.)
Dragon Quest Swords: The Masked Queen and the Tower of Mirrors
- (The models are packed in FPK files and need to be exported using an external program.)
Elebits
Final Fantasy Crystal Chronicles: My Life as a Dark Lord [WiiWare]
Final Fantasy Crystal Chronicles: My Life as a King [WiiWare]
Final Fantasy Fables: Chocobo's Dungeon
Fullmetal Alchemist: Daughter of the Dusk
Fullmetal Alchemist: Prince of the Dawn
Furu Furu Park
- (The models are packed in *.BIN files, but they're not compressed.)
Kamen Rider: Climax Heroes W
Klonoa
Mario and Sonic at the Olympic Winter Games
- (The models are packed in CPK files and need to be exported with an external program. Also, the heads are separate from the bodies for the mid/high-poly models, and both the textures and material properties need to be modified to make them not so dark.)
Mario Kart Wii
- (Use either SZS Modifier or YAZ0Dec.exe to decrypt the files.)
Monster Hunter Tri
My Pokémon Ranch [WiiWare]
- (Files are compressed strangely and need to be extracted using a memory dump from Dolphin.)
Naruto: Clash of Ninja Revolution
Naruto: Clash of Ninja Revolution 2
Naruto Shippuden: Gekitou Ninja Taisen! EX 3
- (Models are small and need to be scaled to 11x their original size.)
Naruto Shippuden: Ryujinki
New Super Mario Bros. Wii
- (The models are packed in ARC files and need to be exported with an external program. Also the models are large need to be scaled to 0.25x [?] their original size.)
NiGHTS: Journey of Dreams
Oneechanbara: Bikini Zombie Slayers
Pokémon Rumble [WiiWare]
- (Files are compressed strangely and need to be extracted using a memory dump from Dolphin.)
PokéPark Wii: Pikachu's Adventure
Rainbow Islands: Towering Adventure [WiiWare]
Resident Evil: Darkside Chronicles
Resident Evil: Umbrella Chronicles
- (The models are packed in ARC files and need to be exported with an external program.)
Samba de Amigo
Simple Wii Series Vol. 6: The Waiwai Combat [Confirmation, please? They apparently have to be extracted from Dolphin's memory dump.]
Sin & Punishment 2: Successor to the Sky
- (The models are packed in ARC files and need to be exported with an external program.)
Soul Eater: Monotone Princess
Space Invaders Get Even [WiiWare]
- ("Just delete the first 8 bytes in red but DON'T delete the others. Then, add 8 F's instead of 12." - Me_Aludes)
Super Smash Bros. Brawl
Suzumiya Haruhi no Gekidou
- (The characters' parts are in separate MDL0s -- body, skirt, hair, left eye, right eye, mouth and eyebrows.)
Tales of Symphonia: Dawn of the New World
My Field of Expertise- (The bone tree seems to be really screwed up, but it works fine when exporting.)
Tatsunoko vs. Capcom
- (The models are packed in FPK files and need to be exported using an external program. Also, the models are small and need to be scaled to 11x [?] their original size.)
Tenchu: Shadow Assassins
Toshinden
Trauma Center: New Blood
Wario Land: Shake It/The Shake Dimension
- (The files need to be extracted from the game's GFA files. Looking into how to do so right now. Also unconfirmed for the moment.)
Wario Ware: Smooth Moves
Wii Fit Plus
Wii Sports Resort
Xenoblade
- (Use this QuickBMS script to decompress the files.)
Yu-Gi-Oh! 5D's Wheelie Breakers
Zack & Wiki: Quest for Barbaros' Treasure
- ("Just delete the first 8 bytes in red but DON'T delete the others. Then, add 8 F's instead of 12." - Me_Aludes)
If you need any other assistance, you can go
here and ask, thats the thread on smashboards that deals with imports