Are believers saved during the tribulation part of the body of Christ?
No. Believers saved during the seven-year tribulation are not members of the body of Christ. They are not included in that company, and cannot be, because the tribulation is primarily a Jewish period of God dealing with Israel, with the temple operating.
Les explains that after the church is raptured, that company of believers is in the Lord's presence in a resurrected state. Then the seven years of tribulation unfold, and during it multitudes of people believe and are martyred, both Jews and many Gentiles. These tribulation believers are not members of the body of Christ; they did not miss the rapture, but simply will not be included in the body and cannot be. In his thinking, 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 connects them with the resurrection of that group of just people, alongside Old Testament saints like Daniel, who stand in their lot at the end of the days, the extra 75 days beyond the tribulation.