"Hydrogen to nickel atomic ratios are up to one"
occurs in the paragraph
"high pressure hydrogen gas at 600 MPa. Alternatively [a surface layer] can be produced electrolytically."
So under normal conditions, the answer is
"0.00005% at 25 °C"
which is the kind of figure expected from most normal materials. If 1 mol Ni could absorb 1 mol H, we would all have fuel cell cars already.
By the way, the Wiki article is written by a metallurgist, but he probably forgot to tell that hydrogen as a hardening agent is impractical because it outgasses too easily. At least steel (nickel should be similar) is freed from hydrogen (which embrittles it) by just 10min at 180°C in a kitchen oven.