Although he is being advertised for several SmackDown live events, it is not guaranteed that Brock Lesnar will be moving to Friday Night SmackDown during the draft.
As noted in the Wrestling Observer Newsletter, the ad department in WWE is usually told things from people that know bits and pieces of what is planned for the future so they would not necessarily know about plans to have him switch brands.
The ads with Lesnar on them for October and November could have simply been done to sell tickets to those shows since they have a lot of weak ticket sale advances.
However, it does make sense for Lesnar to move to SmackDown since it is being considered the “A” show (or at least equal to Raw) beginning next week and it would make a ton of sense to have Lesnar win the WWE Championship from Kofi Kingston since they would want to make a big splash for their FOX debut show.
If Lesnar wins the title this Friday, then that can be seen as another sign that he will be on that brand but we won’t know for sure until the draft. The draft starts on October 11 on SmackDown and concludes on October 14 on Monday Night Raw.