For all its problems, at least this ruling is even possible in the USA. In Australia, by contrast, this would either be ruled as perfectly admissible or, if not, new laws would be put in place by the Federal and various State governments that makes it so.
And that's what the Constitution brings the USA and its people - a law higher than the law enforcement agencies and the governments. At least in theory.
The only problem is that that law does not specify any penalties for transgression, hence there is really very little disincentive for the government and its agencies to respect it. They are free to keep pushing the limits and outright breaking them.
Running an illegal gambling ring is, well, illegal and it is right for the FBI to try to apprehend the people involved. That said, I think that not only should the evidence in question be thrown out - the whole case should be thrown out.
I realise that this is giving criminal a free-pass of sorts but if a law enforcement agency has been found to have breached the the highest law in the land then whole investigation must be considered suspect.
Law enforcement agencies are there to enforce the laws enacted by the various governments - state and federal. In order to do so, they are given limited exemptions from some of those laws. For example, police officers are given the powers to kill their fellow human beings in circumstances outside of the exceptions provided to the common person. They are also given the right to break speed limits and can buy and sell illegal drugs as part of undercover or 'sting' operations. They are allowed to 'open carry' their firearms even in states where laws prohibit civilians from doing so.
BUT, they do not get to break those laws enshrined in the constitution because those laws are above and beyond the laws enacted by the states or by Congress as they are explicitly there to limit what those bodies can do.
As a cop, you get to speed to catch someone speeding and you get to shoot someone who has shot someone. But neither speeding nor shooting people are covered by the constitution. Warrantless searches are covered however and so you don't - no matter how much money you think someone is making in illegal gambling - get to violate the rights enshrined there.
If you are willing to break the highest law in the land then you are simply not fit to uphold the 'lesser' laws. If having being caught abusing children disqualifies you from being a teacher (and it should) then being caught breaking the laws of the Constitution should disqualify you from being a law enforcement agent.
Same logic applies - you've shown that you don't respect the one thing you are asking to be trusted to do.