Here it is mentioned that peanuts should not be raw. Why?
When I will put them in the oven, they will get roasted. Why does that link want me to not use raw peanuts?
For sure, @TFD is correct that you should be wary of Wikihow - in the link you shared, the proportions of ingredients listed at the top don't appear to match the actual amounts of ingredients shown in the pictures.
"Honey Roasted Peanuts" is a catch-all phrase that is used to describe just about any type roasted peanuts in a candy coating. The catch-all extends to recipes that don't even call for much honey (typically a touch of honey and a bunch of sugar) and to recipes that don't even call for much roasting.
To get roasted peanuts in a candy coating using an oven, you either have to roast-then-coat or you have to coat-then-roast. The primary difference is oven time. If you use cooked peanuts, you only need to cook the coated nuts long enough for the candy coating to bake onto the peanut - you're just honey-glazing the peanuts - they won't be in the oven nearly as long as they would be if you were roasting raw nuts. It's a fairly quick process that's easy enough to gauge by sight. Technically, you'd be roasting the honey coating onto the nuts - not roasting the raw nuts in honey.
Note - Planters nuts are labeled as "Dry Roasted Honey Roasted Peanuts" - the peanuts are dry-roasted first then coated then roasted again. Also, for what it's worth, the ingredients list shows they contain more sugar than honey by weight: http://www.planters.com/varieties/nutrition-information.aspx?Site=1&Product=2900007345 .
If you use raw peanuts, you would need to keep them in the oven long enough for the peanuts to roast as well. Given the oven time your link recommends, raw peanuts would not cook - so that would be one fundamental reason why your link specifies that you not use raw peanuts. Potential flaws of Wikihow aside, your link proposes a way to roast honey onto nuts, not a way to roast nuts using honey.
You can certainly honey-roast raw peanuts using more time in the oven - but the timing could present problems with the coat-then-roast method. The candied coating is going to brown as your mixture cooks in the oven making it difficult to visually gauge when your formerly raw peanuts have cooked sufficiently (or if they are cooking evenly). Also, you should be aware that once nuts are cooked and hot, it is very easy for them to go from done to burnt in very little time - it is probably pretty easy to burn your mix if you overshoot the roasting. It would definitely be easier to determine when a honey glaze has roasted onto cooked nuts than it would be to know when raw nuts were finished cooking in a glaze.
But if raw peanuts are easier to come by or if you want to have literally roasted honeyed peanuts, it's definitely possible but I would recommend looking to a more reputable source for guidance (especially for cooking time). And once you start roasting your mix, stir/rearrange the nuts thoroughly and frequently to insure even cooking and to keep burning at bay.