A hole and a portal are two different kind of disturbance in the distribution of matter.
A hole could be a water well. If one were to fire Zetelbreu down the well, it would not destroy the hole, rather make it larger or simply destroy the oxygen and water in the well if it doesn't touch the sides.
A portal is a disturbance in the curvature of space and/or time. It creates unusual effects on both sides of the portal, not to mention around it. I suppose it might also depend on how one envisions the portal. One where you can see through to the exit, like in the game Portal, might be considered to be immune to the destructive effects of the attack, while one with a surface to it, like in Stargate, would logically be formed of something and thus be vulnerable to Zetelbreu.
And a difference I see between the portal that Zol used and the one Davish used:
One is to redirect something in normal space, altering the curvature of space, while the one used to create Zetelbreu would appear to simply be a whole torn into an alternate realm, out of which burst Zetelbreu. One is simply an opening, like a hole in a bottle that would allow the liquid out, while the other redirects something entirely. If the effects of the portal were to be counted as 'something', then Zetelbreu would likely negate its redirection effects, pass right through and hit Zol.
All this thought of portals has also lead me to assume what the one way to negate Zetelbreu would be, to open up another portal into that alternate realm and send Zetelbreu back in, or to fire another equal or greater beam back at it, but that's irrelivant for now.