I have two dwellers, both level 50s, they have the same total SPECIAL stats: 9, 9, 9, 4, 4, 9, 10 respectively but are achieved differently. One wears a rare combat armor (S+3, A+2), and the other one with horror fan outfit (E+4, L+1). This makes the other dweller's 'E' stat a 5+4. All other stats are trained. I have noticed that after sending them both with a 25:20 stim and rad ratio, the one with the horror fan seems to die quickly. Only being able to last a day out in the waste while the other for about a day and a half to 2 days. I'd like to know if stats generated by outfits are in some way different to stats generated in the training room.
There is no difference in stats gained through training and stats gained from outfits... However, the fact that your dweller's base END is different leads to a possible reason why the one with the lower base END is dying faster.
A dweller's hit points is gained when leveling, based on the following formula:
HP Gained = 2.5 + (END * 0.5)
Thus, a dweller with 1 END will gain 3 HP per level, while a dweller with the maximum of 17 END (10 base, + 7 from Heavy Wasteland Gear) will gain 11 HP.
Dwellers start with 105 HP. The minimum HP at level 50 are 252, and maximum are 644.
There is no way to earn missed HP.
Thus, the number of HP that a dweller has depends entirely on how soon your raise their END.