It's not unprofitable. You clearly don't understand it yet.
They can mine any Scrypt coin and Viacoin for free as bonus.
Lots of mining pools do this. Like F2pool and litecoinpool.org
Both mine litecoin and Viacoin at the same time. They won't stop because they get the Viacoins as bonus. Hence the high hashrate. The hashrate doesn't lie. The hashrate of Viacoin up/down moves is similar to that from litecoin. When litecoin hashrate is high, so is that from Viacoin.
Can you help me with one more question, please.
Is it dangerous for mining rigs to do dual mining like this?
Are there higher risks to destroy the rigs sooner with dual mining?
The short answer is no it doesn't cause any additional stress on your mining equipment, with merge mining you are essentially submitting shares on two different chains. Heres a decent short article describing it without getting too technical