Is it just a mulch basin or something like that? I think you'd be fine doing that. Even if your greywater is feeding plants I think it would be OK. If it was a lot of pure urine, maybe not. But since it will be just a small volume of the greywater, and especially if it's just a guest cottage, I can't see the harm. But I'm no greywater expert.
What I'm planning is to have separate pee/poo toilets (I really don't like the "urine diverter" setups I've seen), with the pee drain leading to a
bucket full of sawdust, or maybe into a
straw bale, which when saturated can be composted.