You should be fine.

The aircraft for ET309 overnights in Nairobi, so invariably departs without major delay and gets into Addis on time or early.

When you come into the terminal (either via jetway but more likely bus) there will be ET staff standing there specifically looking for passengers traveling to Accra, Joburg and Maputo. These are the 3 tightest connections and they will process you en masse with priority - sometimes by bypassing the security re-screening, sometimes by a tarmac transfer.

I have colleagues who do the similar ET601->ET809 connection multiple times a month and other than one delay due to late inbound on 601, they have always made the connection with a bit of hustle. ET knows how to make tight connections work in Addis, so just follow their directions and you should be fine.