Not sure that adding him would or should have any impact on the draft possibilities. The potential pick's place on the roster most impacted would be Mason Graham. I guess having Barmore/Allen/Godchaux and then adding Graham is a bit heavy on investment at DT.
BUT... Allen would be 30, coming off injury and in the last year of his deal. Godchaux would be 31 with 2 years left, but a contract set up to move on from next year. Barmore is coming back from blood clots. That's a spot where you can rotate 4 guys through as well so it's not like you can't play them all.
DT would still absolutely be a long term need probably as soon as next year since I think Godchaux will be gone, especially if they add another older guy like Allen. Even Allen becomes more rotational piece than standout as he ages, so it's a starter level need next to Barmore (who is a question mark himself).