For the Packers, I actually look at it as more of a question: Are Hochenson, Fant or Smith value enough to take with a first round pick? I think all 3 will be there when the Packers pick at 12, probably 2 at 30, but all 3 will be gone when the Packers pick at 44.
Where as Warring I think might be better value as a 3rd-5th round pick. Warring has only been playing football for 4 years (started his senior year in H.S.) and was playing in a very run oriented offense at San Diego State, his upside could be pretty big IMO. If the plan is to keep Graham at least another year, Warring would have more time to keep learning.
After coming in small and not having an amazing workout, I definitely think there's a shot that Smith is there in the 2nd round. Being 6'2" 240 is going to take him out of the running for a lot of teams looking for a Y. You almost have to view him as a separate position.
Kyle Shanahan's offense uses a fullback pretty heavily. But he prefers someone with an H Back skill set. That's why the Niners paid significant money for Kyle Juszczyk. Now he lead blocks and catches 30 passes/season. I see Irv Smith as a guy who would fill that role, but with more production in the passing game and more versatility.
As to your first question, yes I would argue that Hockenson and Fant are value enough to take in the first round. Neither are my first choice at #12 and #30 respectively, but both belong in the conversation.
Hockenson would be a great target in a trade down scenario, if that should happen to be an option.
However, the need isn't so dire that they must come out of round 1 with one of those guys. If they go different directions and end up with someone like Warring later, that's great too.