Even if it was hydrazine or UDMH, the half-life of molecules in the upper stratosphere is months/years, anything in the mesosphere isn't coming back down before photolysis breaks it down into NO2, CO2 and H2O. NO2 isn't great for ozone, so hydrazine usage in the mesosphere should be minimized, but not many platforms are using hydrazine still. Oxykero is totally fine.