Can Dark Riku (set 3) equip cards like olympia and others that say "riku"???

I believe so since Dark Riku can use Soul Eater.

Page 5 of the rule book states under card names and Home Worlds:

"Cards with a name that contains part of another card name are treated as that card. For Example, "Riku" and "Dark Riku" are both affected by effects that target "Riku" cards.

Any card that can attach itself to Riku can also attach to Dark Riku, unless it targets a specific type of player such as Kingdom Key.

gangster, thanks guys

Too bad you can't equip OathKeeper to Dark Riku...but he's still powerful with other cards he can equip lol