Deploy SageMaker model to IoT Greengrass in different account?

For IoT Greengrass 1.x, this is possible but not trivial. From the console this is not possible, as you can only select buckets or SageMaker jobs from the same account, but you can refer to resources in other accounts if you use the CLI or the API.

You have to create a new Resource Definition Version with the correct data specifying the model resource and then add it to your group definition. For permissions in the source account, you must set up the S3 bucket policy to allow access from the destination account. For permissions in the destination account, you must update the IoT Greengrass service role policy to access the model resource in the source account.