The abolitionist movement was not simply made up of religious groups, btw. Fredrick Douglass would beg to differ. Along with other former slaves.
However, what was a religious conservative in that time? In comparison to what?
You can certainly say that religious groups in the north were part of the abolitionist movement - but I don't know how you can label them as conservative in relation to other beliefs at the time.
so, how do you go about doing that? what made them conservative in that time?
In the 1700s the Quakers were anti-slavery and were aligned with the atheist, Thomas Paine. So, were they conservative then?
I don't think you can apply the term "conservative" to all religious groups and you need to look at their social beliefs in the context of the time. It seems to me that, by default, any religion that was staunchly anti-slavery even before the American revolution was not a conservative religious group.
On the other hand, the religious groups in the south that used the Bible to try to justify slavery could, following the logic of conservatism as the attempt to conserve the status quo, be considered social conservatives. And religious conservatives, due to the Great Awakening - but the Great Awakening influenced the entire nation - some to positive action and some to negative action.
So, again, I guess you need to provide an explanation of religious conservative in relation to that era for me to say... okay, maybe this is one instance.