Thank you for your question. As I did not know an appropriate answer to give, I sent your question to our in-house veterinarians. This is the response they sent me:
The purpose of the grate is to separate the bird from its own waste, spilled food and other debris. They can certainly survive without a grate but it will become very important that the cage be checked and cleaned multiple times a day. The bird should spend more time higher in the cage on perches anyway.