Yes, many are saved during the tribulation, but not the second half, or Great Tribulation as its called.There will be no revival before the Rapture.
The Church is in the lukewarm Laodecia age, which is the last of the seven Church age characteristics.
In addition, there is much of the Church apostacy occurring presently that the New Testament describes.
However, there will be the greatest revival in human history during the Tribulation...especially during the Great Tribulation.
Multitudes from every ethnicity, country, and language will refuse the Mark of the Beast.
The Two Witnesses and the 144,000 Jewish rabbis will do in a total of seven years what the Church didn't in 2000 years.
Im assuming you are referring to Revelation 7
13 Then one of the elders asked me, “These in white robes—who are they, and where did they come from?”
14 I answered, “Sir, you know.” And he said, “These are they who have come out of the great tribulation; they have washed their robes and made them white in the blood of the Lamb
My understanding of “come out of” means they were saved before the great tribulation.
The great tribulation will bring the most severe judgements and the AC will be fully possessed by Satan, and this wont be a time for the great harvest. Plus, revelation 7 falls in chronologically with the first half, not the second half.
Regardless of when, many will be saved.