As far as the sneak/hide/invis skills are concerned, those skills are not given to a hellion in order to sneak attack people, but to enforce the notion that a hellion could always be watching, or always be right around the corner. Those skills are there to instill fear, not to give an edge in combat as they are often used for.
Everything else I believe that should be true, yet isn't true about some hellions I've seen (Peso's in particular, to be honest, but he is also the only hellion I have directly interacted with much) is summed up in the "code" helpfile, under Honor.
Help code wrote:
Honor:
The Hellion shall value honor second only to strength. Lies and theft are
for those too weak to take what they want or to force their opponent to
submit. For this reason, the word of a Hellion is sacred. To break your
word shows weakness. To attack without issuing a challenge shows weakness,
in that the target must be overcome unawares (like a thief or assassin) and
could not be beaten fairly. The Hellion challenges the opponent so that
the opponent will cede victory due to the Hellion's reputation alone,
compelling obedience. A Hellion should prefer death to dishonor.
Considering that violation of this code is to result in the following:
Help code wrote:
No Hellion displaying weakness in any part of the code shall
command the respect and obedience of fellow hellions, nor meet in council
with them, and may be hunted and punished by stronger Hellions until full
atonement is made. The most extreme displays of weakness may be punished
by expulsion from the order, death, and the wrath of the dark gods
I would think that the code helpfile would be taken more seriously. Instead, I see hellions lying, deceiving, and attacking without challenge over nothing more than loot. Apparently Honor has taken a second place to Equipment.