From the pfsrd:
An unseen servant is an invisible, mindless, shapeless force that performs simple tasks at your command.
"Force" being the operative word here, as well as "shapeless." It seems at first blush that Unseen Servant is a magical force with enough programming to be able to do what you tell it to. In other words, think of it like telekinesis except you have to tell it what to do.
I suppose with an extremely literal interpretation it is possible to see the Unseen Servant as... perhaps, a body of colored gas? The word "shapeless" seems definitive to me as "something you simply cannot see as it does not exist materially," but I suppose that's open for interpretation.
So in other words, you could almost make a case either way to your DM. The most RAW, literal version would say that because the servant can take damage, has 6 hit points, has a speed, able to make checks etc. it is a creature (if it walks, talks and looks like a duck...). And, being just an invisible creature on the same plane as you, there is no explicit reason why you shouldn't be able to see it using See Invisibility.
If you switch to an RAI angle, however, it seems evident from the lack of description regarding the servant's true appearance and its description as a "shapeless force" that the servant is akin to, say, an independent Mage Hand. This doesn't have any real evidence backing it, but it is more convenient in most situations since nobody knows what the Unseen Servant is supposed to look like, if it even has an appearance. Since it seems like you're trying to keep tabs on your mischievous apprentice, however, it may not be convenient for you.