I recently contacted both DJI and the Reseller I purchased by Osmo Mobile from about a problem with the device. The reseller wants me to use Gradus Group for the return. Is that the same as going directly to the DJI repair center?

I'm guessing Gradus Group are the distributors or suppliers to the reseller and the reseller is redirecting you to Gradus Group, hoping to speed thing up. Gradus Group may have to forward the device to an authorised DJI repair centre for repairs, unless they are authorised for repairs etc.

Sir, can you please explain what Gradus Group is? Is it one of the distributors like Cat824 said?
Besides your dealer, you can also contact our support to start a ticket and send in for evaluation and repair directly.Please let us know if you any further queries. Thanks.