According to this youtube video it is in Fire Red/Leaf Green:
https://www.youtube.com/watch?v=BD8ByEITQkg
Note how the truck is still there and that the player picks up an item. This could reinforce the idea that it really was used to supply the ship.
I wonder, do any of the telescopes talk about the SS Anne? Like the ones between Fuchsia and Lavender?
The reason why this Pokemon truck is speculated? The pokemon games are very light on sprites! Unlike other RPGs Pokemon isn't noisy graphically. Games like chrono trigger or Final Fantasy, you will see things everywhere that do nothing: this can be books, rugs, boxes, crates - anything. In Pokemon, you tend to think something will do something because the game is relatively bare!