You can use your USD to buy Bitcoin and proceed to buy NEO on many sites that accept NEO Trading. That is quite simple and you can do it without worrying at all. Do it yourself and you will continue to buy other altcoins.
Im asking if i can buy it directly with USD without having to convert coins
Exchange Livekoin provides an opportunity to buy coins with the help of fiat currencies. You can choose a convenient way to replenish the options listed there. Including usd.