I understand what you're saying. Here's the issue.
The
IC does indeed gain Scout and Stealth. The
IC alone can make a scout move and gains stealth. Both the Scout and Stealth special rule say that a unit with at least one model with the special rule has the ability. If the
IC had the ability in it's own right, it could certainly benefit the unit with Bulky or Very Bulky models.
However, in your example, the
IC is gaining Stealth and Scout
not on his own, but
because of another special rule, in this case "Strike from the Shadows".
And that special rule
clearly states that units with Bulky or Very Bulky models do not benefit from the rule, which would include the
IC at the moment he joins the unit.