What extra conditions?
Krakoa is not demanding anything because the UN usually operates that way with every country, each country can handle itīs criminals the way they chose to unless they have foreing criminals, in that case there must be an agreetment between nations to decide how to handle the situation of a particular criminal. Itīs a legal matter not a matter of trust.Im not saying that what they are doing is illegal but the UN have no voice in this, once the mutant criminal is take it to Krakoa you lost track of what happens there. In practice Krakoa demands blind trust in how they handle the criminals.
The UN doesnīt have the authority to force countries to operate the way the UN wants but they can make a suggestion or in the case of a very serious situation, meaning a military intervention or war , it can seek the cooperation of other nations to try to put a stop to it.In the case of the MU they could call on the Avengers and Shield if it comes to it but as long as Krakoa keeps itīs bussines for itself then thereīs no reason for the UN to act that way.
I call them embassies because they are supposed to be the place in which they conduct bussines with the countries in which that gate is located and also the place of contact for their citizens. Thatīs how an embassy usually operates, they are considered part of that nation inside another nation territory with permission from the host nation, they can reject that embassy and itīs ambassador at any moment but this type of decisions are only considered when the relationiship has become hostile or cold. There are countries who have more than one embassy for each country in which it has a political relationship, so no, they are not borders in the traditional sense.The gates are not an embassy because they are an actual border with another country. A border that you cannot control and that in some cases like USA, there are several of them.