Yeah, the tooltips for the HCL pieces does kinda make it seem like only 350+ leatherworkers can wear the pieces/set, but any druid (of any profession) can wear the entire Heavy Clefthoof set.
In fact, the bonus that 350+ leatherworkers get when they equip all three pieces is +20 strength. It's allright, but not all that valuable for tanking. It'd be much more compelling as +20 stamina or even +20 agility.