Are tribulation believers part of the body of Christ?
No. Tribulation believers are not members of the body of Christ. They did not miss the rapture; they simply are not included in the body and cannot be. They belong with Old Testament believers, since the tribulation is God dealing with Israel, a primarily Jewish period with the temple operating.
Les explains that after the church is raptured, the seven-year tribulation brings multitudes to faith, and many are martyred, both Jews and Gentiles. These believers are not members of the body of Christ; they did not miss the rapture, but they simply are not included in the body and cannot be. Les places them with the Old Testament believer because the tribulation is the time of God dealing with Israel, the temple is operating, and it is primarily a Jewish period. He puts the whole lot of tribulation believers and Old Testament believers into the resurrection of this group of just people, with Daniel and Old Testament saints standing in their lot at the end of the days, the extra seventy-five days beyond the tribulation.