Using latest AM v8.0.2 with latest t-rex-0.17.2 which added ethash algorithm for Ethereum. Had to manually enable algo ethash in Managed software options.
Diagnostics when starting t-rex with -a ethash :
...
20200918 14:50:26 WARN: failed to subscribe, JSON-RPC call failed: member "id" is null (original json {"id":null,"method":"mining.notify","params":["91fd","0xc01057f1394d2505a01d2310e4843abf45806d85c2e0cee45e46c17dfcec76ad","0x8552ce848ce6b5e0b813e271bd44862eda17e35032821ba00a44f2e4ace34fcd","0x000000007ffffffe00000007ffffffe00000007ffffffe00000007ffffffe000",true]}
)
20200918 14:50:26 ERROR: No connection, retry after 10 seconds
Hi Patrik,
the new version of T-Rex mining Ethereum at NiceHash needs a special prefix:
"0.17.2 * Add "ethash" algorithm (for Ethereum). For Nicehash mining use "nicehash+tcp://" pool url prefix."
I know in Online Services / Properties. But how can this be done, if we also want to use other miners than just T-Rex for Ethereum at NiceHash? These other miners would also get the new prefix which should not work. And T-Rex will not work with the standard prefix. Is there a workaround or can you do some magical auto detecting tricks here for that case?

With the latest definition update I've mapped "ethash" for T-Rex miner.
For Mining Pool Hub, it looks like some incompatibility between the T-Rex miner and their Ethereum pool.
The Nicehash, this requires a small code change in Awesome Miner to change the protocol to "nicehash+tcp" as you pointed out. This will be part of the next release.