My personal, and probably not universally, held opinion.
The Bitcoin stackexchange site is for questions about technologies that support the bitcoin currency. That includes on-chain transactions, but also other layers.
Omni, in my view, does not support the bitcoin currency. Rather the opposite, it uses the Bitcoin blockchain to support other assets. I consider that usage parasitic: if it provides any value it's censorship resistance for those unrelated assets, and does so in a way that forces costs onto Bitcoin infrastructure without providing benefits to the bitcoin currency.
I think a grey area exists for questions about Omni's interaction with the Bitcoin blockchain. However, almost all Omni related questions I see here are specifically about support for some other token, and those should definitely be off-topic in my view.