I don't know if the ranger skills get a damage bonus based on stats. I've got saves with plenty of spare stat points, so could probably test that in a couple days, or so.

With my ranger I went primarily with dexterity (with some strength and vitality, no spirit or intelligence). In DKS there are several unique bows you can buy, which focus more on ranged damage, so get the majority of their damage bonus from dexterity. I didn't pay too close attention to the damage ranges on random magical bows, but I didn't see anything (normal, balanced or magical) that came close to the unique bows.
You'll also probably want to get your dexterity up at least somewhat to help with critical hits.

The ranger skills require mana, but I found between equipment bonuses / enchantments and (eventually) the Mana Efficiency skill I didn't need to put any stat points into spirit or intelligence.


Poison Arrow I boosted before the Battle Tower, but only put 1 skill point in after unlearning my skills. I tried Stun Arrows after finding some jewellery with that bonus, and put a point in myself; it is quite helpful early in the game.

Once you put a few points into Splitting Arrows, it pretty much becomes a 'die' button for most opponents that get close. That and Explosive Arrows you will probably want to max.


I described my ranger playthrough in the topic Who's playing DKS on nightmare difficulty ? (which you've already seen).
From my (currently) second last post in the topic, I quoted my stats and skills on level 37:

At the end of the Hall of Echoes, I had 98 unused stat points (base stat values the same as they were at level 15), and 21 unused skill points.


Code
equipment            with  without

hit points           942     306
mana                 639     222

Code
vitality              53      14
spirit                22       2
strength              21      21
dexterity             51      36
intelligence           7       7

Code
damage              281-425
magic damage        114-133
melee resistance      22.1    10.4
ranged resistance     38.5    16.6
magic resistance      37.2     3.7

conditioned body      21      21
heightened reflexes   74      36
indomitable will       7       7


Skills

Ranger Strength - 10
Explosive Arrows - 6+8
Splitting Arrows - 7+3 : these 3 I should probably max soon

Poison Arrows - 1
Stun Arrows - 1 : secondary skills

Death Blow - 1
Evade - 1
Healing - 1
Regenerate - 1 : tertiary skills

Lockpick - 5
Ranger Stealth - 5
Mana Efficiency - 6
Mindread - 15 (1 up until shortly before entering the Hall of Echoes)


Before the battle tower I had a couple points in Poison and Stun Arrows, as well as equipment bonuses (recently replaced some +2 Poison Arrows earrings). Both still come in handy, but mostly just as a way to pause and select a specific target, then come out of pause attacking (a normal ranged attack doesn't unpause the game).

I'll probably boost Death Blow when I have lots of skill points I don't know what to do with, and after that possibly Regenerate, then Healing.
Lockpick will get maxed when I can raise the level cap. Unless I start upgrading to equipment without mana bonuses, I will not need to invest any more into Mana Efficiency.