I would have to disagree, if you use Gate as a Calling spell, then the creatureisconjured.
On pg 157 of the players, in the Calling section, it states that Magic Circles do work with "Spells that call powerful extraplanar creatures...". Gate is a Calling spell, so it would qualify.
**OTOH, by analogy with the 'prison' configuration, it would be reasonable to treat the circle itself as a barrier that is impenetrable in one direction (for conjured creatures).**
I do agree with this. But, it's unclear one way or the other, especially with a spell like Unhallow. Is just the periphery so protected?
**And by extension from the alignment issues with the 'untouchable' effect of the Protection From [Alignment] spells, the barrier would only affect conjured outsiders of the correct alignment.**
If you mean that a Protection From Evil only protects vs evil aligned conjured or summoned creatures, I disagree. The description sees to make no such mention. I agree with Urbanmech. If it's a magic circle vs. evil, then only Good conjured or summoned creatures could penetrate the barrier.