We perceive what happens (ie., Unown's emissions), from Suicune's perspective, but I believe that the point of this is mostly to show that something is going on in the Ruins of Alph. Could the Unown be feeling that the GS Ball is close to opening? Even so, what do the Unown have to do with the Pokémon sealed in this Poké Ball? And why was Suicune alerted when it wasn't involved at all in the event on which Celebi appears in the Ilex Forest, presumably time-traveling with Ethan/Kris? Perhaps Suicune's (and the other Beasts'?) role was to find a Trainer worth entrusting the GS Ball with, and the opening scene possibly leads to the Beasts' gathering in the Brass Tower?
Still, although this is not very far fetched, it's kind of regretful. I prefer to associate Celebi with Kris rather than Ethan, and by this theory, Ethan is supposed to obtain the GS Ball (if that indeed leads to the Beasts' gathering). An alternative theory would have the Unown foreshadowing Arceus's coming, although this is very retroactive, and still hard to believe, considering that Suicune doesn't have anything to do with Arceus, and that's not a reason for them to be restless either.
What I prefer to believe is related to what I said earlier. We have Suicune's perspective of the event, but this technique is used to bold the importance of what is happening, showing that even a Legendary Pokémon is alerted. The Unown being restless foreshadows something (plausibly, related to the opening of the GS Ball), but it simply warns Suicune, in contrast to directing it. This can be backed up by the fact that Suicune's (and the other Beasts') roles were not cut short in Crystal, and we actually learned a lot more about them, while also seeing Suicune's pursue in finding a worthy Trainer.
Still, although this is not very far fetched, it's kind of regretful. I prefer to associate Celebi with Kris rather than Ethan, and by this theory, Ethan is supposed to obtain the GS Ball (if that indeed leads to the Beasts' gathering). An alternative theory would have the Unown foreshadowing Arceus's coming, although this is very retroactive, and still hard to believe, considering that Suicune doesn't have anything to do with Arceus, and that's not a reason for them to be restless either.
What I prefer to believe is related to what I said earlier. We have Suicune's perspective of the event, but this technique is used to bold the importance of what is happening, showing that even a Legendary Pokémon is alerted. The Unown being restless foreshadows something (plausibly, related to the opening of the GS Ball), but it simply warns Suicune, in contrast to directing it. This can be backed up by the fact that Suicune's (and the other Beasts') roles were not cut short in Crystal, and we actually learned a lot more about them, while also seeing Suicune's pursue in finding a worthy Trainer.