Definitely not ethical. The obvious intent of a demo/trial is that it be available for an evaluation period, then disabled or crippled until it is purchased.
Note that a trial version's EULA might prohibit it from being used for commercial purposes anyway.
As @reinierpost commented, you can't know if it's legal without reading the EULA - they may mention reinstallation explicitly.
Even if it does look like there's a loophole because virtualization or reinstallation aren't explicitly mentioned, it may just be that the EULA's legal language hasn't caught up with the technological landscape yet. In that case, if it goes to court, it'll be up to someone else to decide if it's legal or not - and unintentional loopholes are not likely to stand up to serious scrutiny.