The UK courts will permit extradition to the US if the alleged conduct would have been illegal in the UK regardless of what the offence is called in either country.
Well I think that it is difficult for the extradition to occur in the case someone is charged in the US for something that is not a crime or illegal in the UK.
I’m not sure on this but despite any bilateral agreements, most EU countries cannot extradite someone for something that is not a crime in that country, and also cannot extradite for something that is a crime on US and is only illegal (but not crime, only punished with fines) on that country.
In the case of an information portal that is hosted outside the US it would also be difficult to say that you are engaged on an illegal activity, since although some americans can visit the website, it can be a general site not particularly dedicated to US market, and with the most important casinos not accepting US wagers, there is no link.