A lot of the "Christians" who do not believe in Jesus as God use a different book other than the Protestant Bible, so we need to keep that in mind. For instance, the JWs and the Mormons use different books. So I agree that these nonbelievers fall in the same category as other religions such as Muslims, Jews, Hindus, etc. Just because they "almost" believe what we believe doesn't cut it, they might as well believe something very different. Knowing this, I believe all these groups fall under the category of never hearing the Gospel and/or not understanding it, rather than knowing the Gospel and rejecting it. I believe God will judge them accordingly based on knowledge and conscience (there are verses in the Bible to support this that I have posted in other threads). Like, I believe pastors will be judged more harshly than people who didn't know Jesus (or know Him very well).
Luke 12:41-48
New International Version
41 Peter asked, “Lord, are you telling this parable to us, or to everyone?”
42 The Lord answered, “Who then is the faithful and wise manager, whom the master puts in charge of his servants to give them their food allowance at the proper time? 43 It will be good for that servant whom the master finds doing so when he returns. 44 Truly I tell you, he will put him in charge of all his possessions. 45 But suppose the servant says to himself, ‘My master is taking a long time in coming,’ and he then begins to beat the other servants, both men and women, and to eat and drink and get drunk. 46 The master of that servant will come on a day when he does not expect him and at an hour he is not aware of. He will cut him to pieces and assign him a place with the unbelievers.
47 “The servant who knows the master’s will and does not get ready or does not do what the master wants will be beaten with many blows. 48 But the one who does not know and does things deserving punishment will be beaten with few blows. From everyone who has been given much, much will be demanded; and from the one who has been entrusted with much, much more will be asked.