LIN movement (with reachable coordinates/axis) possible or not?

As a general rule, LIN motions are used only when necessary, and PTPs at all other times.

It's less a matter of a LIN move being possible, as much as it is a matter of a LIN being advisable. For example, as a LIN motion approaches the wrist singularity, the motion becomes increasingly difficult, but the motion does not become impossible -- rather, the robot is forced to reduce speed a great deal while counter-rotating the wrist axes to compensate. That said, since an iiWA lacks unlimited-rotation axes (unlike it's industrial cousins), a LIN motion is at more risk of encountering the axis limits. OTOH, the 7-axis nature of the iiWA grants some additional flexibility which can, sometimes, be used to counteract this problem to a degree.

PTP motion commands predict failure before the motion begins, but LIN motions do not. PTP motions look ahead to the planned motion destination and evaluate it before moving. LIN motions are essentially a series of tiny PTP motion steps, and only look ahead one step. As such, a LIN motion whose end point is unreachable will execute until it strikes a limit, even if that end point is unreachable.

Neither motion type pre-checks the path between the current position and the destination. PTPs simply don't care, and for LINs it's simply not practical. So even a LIN motion that should be reachable can suffer from a "can't get there from here" problem.

Generally, LIN motions should be used as seldom as practical, should avoid axis singularities, and should be "bracketed" by PTP motions that are used to pre-set and post-set the axes correctly.