In my opinion, no, you don't require new tiles to make a great hack. Sure, it makes it look good, but I only believe in hacks that are based of their features, storyline and scripts, that's what makes it a lot more interesting.
I find it hard to find the right tiles for a hack, and find it hard to insert them the "right" way, so I normally use the normal FR tiles, and maybe do some changes there and there. However, I'm kinda a perfectionist, so if the tile isn't perfect, I simply won't add it. :/
If you can't insert tiles, then don't. But if you can, but don't want new tiles, then don't.
It's your hack, it's your choice.
I've also noticed that when people are looking at screenshots they only care about graphics, and if it isn't good enough, they leave and don't bother. (I'm not pointing at PC members, but lazy visitors, etc.)