Of course. Even a 3% stake of a public company means that they have some kind of influence. No one is doubting that. And to be sure having even that much investment in a company means that Samsung can use it to "vote" on key internal decisions and strategic directions within Sharp. They can also wield it to buy or push influence to the other 97% investors. The reality is that the majority of those other investor-owners are most likely entrenched Japanese millionaires, and culturally they would frown on being "taken over" by a symbol of Korean industry.
But the point is, 3% is still nowhere near a controlling interest of a huge multi-national company. It would be different if (for example) Samsung suddenly attained 40% or 45% ownership of Sharp. Now THAT would be tantamount to (approaching) a takeover, and hence would be Panic Time for Apple (assuming they had not found alternate suppliers already).