Just testing with the Aid spell, and I noticed a few things:

1. It is possible to cancel the "Extra Hit Points" effect. This did not lower the character's HP down to normal. (It did, however, prevent Aid from re-rolling the bonus hit points for some reason.)

2. The "Extra Hit Points" effect lasts longer than the "Bless" effect. Much longer; I think it may last over a minute of holding down Alt+F12 on the keyboard.

3. In neither case did the character's HP go back to normal, even after waiting a while while holding down Alt+F12.

So, does that mean that "temporary" hit points aren't really temporary in this game?

I have noticed that so many AD&D based games get this wrong. There's Dungeon Hack with its permanent stacking Vampiric Touch, the Infinity Engine games where temporary HP is implemented as a combination "increase max HP" effect and a healing effect (with the healing being as permanent as Cure Light Wounds is), and even Temple of Elemental Evil, which I consider the most accurate implementation, allowing False Life to stack and having Vampiric Touch be broken and useless.

(The old Gold Box games avoid this problem by not implementing any effects that give temporary HP in the first place.)

Did a bit more testing (by setting everyone to AI control and holding Alt-F12 to win the first arena battle in record time so that I could get an injured character) and the way Aid seems to work is as follows:

1. Adds Bless effect
2. If HP > Max HP, HP = Max HP
3. Add 1d8 HP

This means that Aid can, indeed, be used as a healing spell. Multiple castings will stack as long as HP isn't above its normal maximum.

It also means that, if the target's HP is above her normal maximum, casting Aid can actually lower the target's HP.

Note that Life Draining and Vampiric Touch likely work the same way, minus the Bless effect, of course.

The "Extra Hit Points" effect that you get doesn't seem to do anything.

Does Wake of the Ravager work the same way?

I'm not surprised at all. This is one of those obscure powers where the functionality is so different and the effect so weak, the developers didn't see any reason to implement it faithfully.

To put it in perspective, Aid was probably written that way in 2nd Edition so it was "not just another healing spell." To code it in a computer game requires keeping track of a second HP total granted by the spell. Since tracking more than one copy of any stat is prone to bugs and exploits by gamers, it's not surprising a lot of other games avoided this one.

In the Dark Sun games I believe Aid = Cure Light Wounds + Bless + some variable spillover HP (just tested this briefly). On stacking it, the spillover just gets re-rolled. That's a reasonable interpretation of the P&P text, given that after most battles a resting point isn't hard to find.

Ravager appears to work the same way, and should for every spell afaik. Ravager should generally be a strict superset of the Shattered Lands' spell engine.