Pilgrim
Researching this issue a little more, I would conclude that James White as well as most of the Theologians that I respect, would wholeheartedly agree with Sproul on this issue. In fact, unless I misunderstand him, even CH Spurgeon would say similar things. Similar things could be said about Whitefield for believing John Wesley was a genuine Christian.
Although Outside the Camp takes a very hardline stance on this, especially with their "Wall of Shame." It appears that they are not the only ones who take a similar stand. Some state that to be a "tolerant Calvinist" is an oxymoron and proves that they really do not understand soteriology and therefore there is reason to doubt their salvation. Others say that while it may not necessarily mean the person is not saved it does mean that they are not consistent with their own theology.

Tom