Nice find! Got me to check Hawaii papers- had never heard of this before, though now that I've read up, I'm not surprised. It almost rings of truth, after all there were missionaries from New England that came to the islands; the ABCFM most famously- yet their missionary activities were well over before 1900 with nearly the entire surviving population converted to Protestant christianity, with smaller numbers Catholic or Mormon. The senators purported descriptions of Hawaiians is also pretty odd considering the high literacy rates on the islands, the electrical power, and the phone system- things that would have been novel to many Americans at the time.

Here is a reply printed in the Pacific Commercial Advertiser.

Later on it seems Sen. Burton retracted or denied his statement; see here. This articles come from the wonderful online archive at Chronicling America.

I can only speculate that when he visited Hawaii, someone complained about the wealth or land holdings of the descendants of the first missionaries- many of whom- far less scrupulous than the original couples that came to the islands (though not all of them were saints)- profited greatly from their families' position in society. Or, that the quote was entirely made up or taken out of context.