I find it amusing that it was Calvinists and Presbyterians who came up with the "Five Fundamentals" (where the pejorative "fundamentalist" comes from) as an ecumenical tool to find common ground with Christians of all persuasions (including Catholics and Pentecostals). Every church and Christian has "unbiblical" beliefs to a lesser or greater extent, at some point in their life. The five fundamentals establish a common foundation as to which beliefs matter most, i.e. are non-negotiable. So long as the Pentecostal congregation in question agreed with the five fundamentals, I see no reason why the OPC congregation in question wouldn't be willing to rent space to them.
That said, it's the Catholic Church, not the Presbyterians, that makes theology an "all or nothing" issue. Case in point:
"....If a Catholic rejects even one tenet of Church teaching then they are as a result declaring that the Church is not a holy institution and more importantly the Churchs belief in truth is wrong....Catholicism has a monopoly on the truth, it is not good enough to only believe in some of the Churchs teachings, we have to and are logically required to believe in all of the Churchs teachings."In this mindset, to be a "real" Christian is to be Catholic. And to not be Catholic is to be a member of an "ecclesial community" (Protestants), a member of a "defective church" (Orthodox), or not be a Christian at all. The mindset of Catholicism towards any corporate exercise of Christianity is exclusivist by design. People are either (already) Catholic, or are "generally hellbound" as one FReeper put it to me.
-- from the thread What Is The Catholic Truth?
So for someone inside the Catholic mindset, when they look upon Protestant denominations, they project and think that a Protestant denomination must be exclusivist towards any other denomination. They think that Protestants exclude all denominations/members not their own from the full body of Christ and from Heaven, because that's how the Catholic mindset approaches all others. While there are some "Protestant" congregations and denominations (I'm using those terms loosely) may act that way towards outsiders, the majority do not (and the creedal ones IMO less so).
I'm guessing it's this Catholic mindset re exclusivism that's giving you trouble in understanding how an OPC church can share it's space with a Pentecostal one.
hardly — the OPC says clearly that there is no point in ecumenism with groups such as many pentecostals etc.