No DC will get through, but 50Hz AC will jump across just like the RF. Well, not so much jump as influence. 240Volts of mains going through the isolator wouldn't put 240volts the other side, maybe a 1volt 50Hz wave would get on it though...
As to neutral and earth being swapped around, it will work. Most houses have PME earthing, where the earth wire is connected to the neutral wire at the meter anyway. The purpose of the earth wire is if the live comes in contact with the case, it will short circuit, causing the fuse to blow. As long as the case is connected to SOMETHING that creates a circuit with the fused wire, then the fuse will blow on contact.
If you have RCD circuit breakers (MCBs work in the same way as fuses) though and have neutral and earth swapped around, they will trip immediately, due to the high imbalance between live and neutral. A mate of mine once spent 3 hours trying to work out what was going on as his new RCD kept tripping. Turned out that one of the ring mains in his house had the neutral and earth cable swapped around in ALL the sockets on that ring
- and had been like that for 20 years or more since (he'd only lived in the house a few years). Re-wiring the sockets then stopped the tripping. But it had worked fine for 20 years or more.
The earth wire (and hence neutral due to PME) here is approximately 70 volts above true ground. Makes a few things buzz nastily.