If Life Orb being used then yes as the IVs are for Life Orb numbers.
Ah ok, I want to run some simple math by you to see if I'm thinking about this correctly. With no HP investment and a 31 IV in HP, Excadrill reaches 361 at lv100. 29IV = 359 HP at lv100. This satisfies:
HP = 10(n) -1 where n is any natural number. Latios and Genagr, who also commonly have 29 IV's recommended in their sets, reach 299 and 259, respectively. So then a Life Orb number is any number that is one less than a multiple of 10 and thus allows you to attack 11 times instead of 10? (assuming no prior damage). And so the reason that 31 is inferior to 29 in this case is because 10 attacks leaves you with 1 HP @ a 31HP IV while 29HP IV leaves you with 9HP?