He says he uses one all the time, just leaves it on the lens - even in the house
Sounds like he can't tell his polarizing filter from his UV "protection" filter to me. Sadly a lot of shop staff these days are hired to sell products and thus often don't actually know the subject area they are dealing in that well (but just enough buzzwords to flog stuff to shoppers).
As for a macro lens the Nikon 105mm macro is certainly a very good choice - good working distance whilst also having VR which whilst not as good at macro distances its certainly a good feature to have in a lens and will help out with longer distance work as well.
The other macro primes on the market are also good options - infact there is very little difference between the macro lenses on the market at the moment in terms of image quality. Though studio tests might show some differences sample variation is going to be more of afactor and in the field you would be hard pressed to tell one lens's results from anothers.
Overall then the other options: (suitable for insect work and thus at least 90mm or longer in focal length)
Tamron 90mm macro; Tokina 100mm macro; Sigma 105mm macro; Sigma 150mm macro; sigma 180mm macro; nikon 200mm macro (I think this is a true macro lens but I have seen very very few users of this lens so I am not sure how valid a suggestion it is a macro shooter from nikon might know more)
The 90mm, 100mm and 105mm options are all good budget line choices - cheaper than the 105mm VR nikon and whilst optically very good they are slightly lesser in key features (generally slower af and such - though af on macro lenses in general is slow).
The 150mm and 180mm options are both a cut above the other brand options and have some very nice features (internal focusing, sigma teleconverter compatabiltiy and HSM focsuing) which make them popular choices with many insect shooters.
Give them at try in store though and see how they feel. Also do consider lighting as well - a good speedlite flash with a softbox (eg a lumiquest softbox) is a good start and a generalist speedlite flash will have a lot of uses outside of macro work (unlike ring and twinlight flashes which are more limited in thier use outside of macro work)