WWE could go this route and it's possible they would if Mark Hunt was a huge name. Hunt has a record of 12-10-1, not exactly the stuff that dreams are made of, but he's done pretty decently since coming to UFC. He's 8-3-1 in the UFC and has won various bonus awards like Knockout, Fight or Performance of the Night. Neither Hunt or Lesnar are in their prime; Hunt turned 42 in late March of this year while Lesnar will be 39 come about mid July so the novelty of Lesnar returning is what would be the draw for their fight as it may be one of Hunt's last big fights and Lesnar's doing it for a huge paycheck.
I don't think most WWE fans know or care about Mark Hunt regardless of how Lesnar's fight with him comes out. Samoa Joe is 37 years old and he's another one of these guys like AJ Styles and Bobby Roode, that may well have waited too long before deciding to go to WWE. Prior to his arrival in NXT, Joe hasn't really been on the radar all that much for the past few years whereas AJ Styles had a highly acclaimed and successful run in New Japan; as a result, Styles is the one with the buzz and is generally the bigger star which is why he went straight to the main roster rather than NXT. The longer Joe stays in NXT, the less likely he's going to find major success on the main roster if he's even brought up to the main roster. If he does make it to the main roster, I can see him in the mid-card or tag title scenes; I can see him getting into the main event picture, possibly, but I think the odds are stacked against him winning.
Seeing Joe against Lesnar strikes me as mostly just using Joe as a sacrificial lamb. I don't see it doing much for him in terms of a push or a rub so much as it'd be about keeping Lesnar looking like a monster. Since his return to WWE, Lesnar has ultimately gotten the best of everyone he's feuded with, including the likes of John Cena and the Undertaker. Given that Lesnar has conclusively beaten the "face" of WWE and the flag bearer of WWE, I don't see Samoa Joe as someone who'd wind up winning if he did face him. Truth be told, I have a feeling that, if anyone, Lesnar will ultimately be taken down by Roman Reigns because Vince's mind is made up and his course is set: he wants Roman Reigns to be one of the biggest names, if not the single biggest name, in WWE for the next 10 years. It's exactly what many fans simply do not want to happen, but the only way I see it being derailed is if Reigns does something to garner major heat, Vince steps down as CEO by choice or by circumstance in which a new final creative authority steps up who isn't so certain about Reigns or if Reigns becomes injury prone or suffers a big league injury that puts him out for good.