If the ATV3 does get native Hulu support, it will be for likely be Hulu Plus only, not the free Hulu you can get online, meaning you'll have to pay a monthly subscription fee to use it. (Hulu states that Hulu Plus is for TV-connected devices, while the regular Free Hulu is only for use on the computer. See here:
http://www.hulu.com/plus-?src=topnav
Also it's been possible to get Hulu (both free and paid versions) on the current ATV2 for over a year now. It involves jailbreaking, but is not difficult and costs you no money. Instructions are here:
https://forums.macrumors.com/threads/1305573/
Of course, at this point you should definitely wait since the new ATV3 will likely be out in just over a week. But even then, it's likely to be jailbroken at some point and then you'll likely get free Hulu access on the ATV3 at that point.
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This, PLUS the reduced inventory is NOT THE ONLY INDICATOR. At this point MR has posted other evidence suggesting the ATV will be updated alongside the iPad. (item model number, rumors from insider sources ala 9to5mac, etc.)
I think the people here who are saying that inventory ALONE is not a decent indicator of an imminent refresh are technically correct. But a confluence of evidence INCLUDING low inventory, new part numbers, a confirmed upcoming Apple event, and insider leaks and rumors, all taken together, ARE a decent indicator.