Are the four horsemen of Revelation also seals?
Yes. In Revelation chapter 6, the four horsemen are also seals among the seven seals on the scroll. The context states that all of these horsemen were also seals, and that four of the seals had been opened, with seven seals to begin with.
Les explains that in Revelation chapter 6, the horsemen and the seals are the same. He notes that four of the seals have been opened, and there were seven seals on the scroll to begin with. When the fifth seal is opened, John sees the souls of those slain for the word of God and for their testimony, which Les relates to the tribulation martyrs. He also teaches that many non-Jews will be saved during this seven-year period but will not live long, being martyred almost immediately.