Is the church present during the tribulation according to this teaching?
No. The tribulation is primarily God's dealing with the nation of Israel, not the church. The church cannot be mixed up with Israel during the tribulation, because that period is God's dealing with Israel. Scripture affirms God will never cast off Israel.
Les teaches that you cannot let the church go in and mix up with Israel in the tribulation because it is God's dealing with Israel, not the church. He points to Jeremiah 30 and 31, where God promises He will never cast off the seed of Israel; the tribulation is primarily God dealing with the nation of Israel. While individual Jews can be saved in the age of grace, the church is not to be mixed with Israel in that future period.