How would the thinkers of the Enlightenment regard the ideology of Conservatism?
This depends on the context since the meaning of conservatism varies with the context as well.
For example, Enlightenment thinkers would not have thought well of a conservative like Edmund Burke. They would have disliked his reflexive respect for tradition. The reason for this is that they would have believed that following tradition was irrational. Tradition gave us such things as monarchy and aristocracy, neither of which was compatible with Enlightenment views.
By contrast, Enlightenment thinkers would probably regard conservatism today much more positively. An American or British conservative today is not pushing for monarchy or for less democracy. Today's conservatives believe very much in the basic ideas of the Enlightenment such as individual rights and limited government.
Therefore, the answer to this question will depend on which sort of conservatism we are being asked about.