It's designed for that. There's another 20 amp available for the rear AC. So when you're running your genset you can run both ACs...but...that's all it's connected to, the rear AC, in most 30 amp rigs.
And of course they (Onan) fudges the numbers, you get 50 amp when the output is 110 Volt AC. Generally, it's not set for that, it's actually set for 120 volt which is the USA standard. Generally, it can only supply a strong 45.8 amps.
If your EMS is showing 50 amp, that's cool, that's what you're getting so go with it.