What Christian denominations accept the idea of a pre-Genesis creation? Some Biblical Scholars insist on a pre-genesis creation in which the angelic beings were made, this creation pre-dates the 6 day creation of the 'heavens and the earth' mentioned in Genesis 1:1.

This idea comes from the Book of Job:
Job 38:4 - "Where were you when I laid the foundations of the Earth; tell me if you know so much... (7) while the morning stars sang together and all the angels shouted for joy?"

We are clearly told here that intelligent beings existed prior to the creation of the Earth and of Adam. Much debate exists concerning exactly when the angelic beings were created. Which denominations support an angelic creation event prior to the Genesis creation event?
Though I am not sure I can speak for an entire denomination, I do have a major in Bible from Free Will Baptist Bible College, so I can say the denomination educated me.  With the preliminaries out of the way, one must consider that there is no mention in any form of the Genesis account of the creation of Angels.  That leaves two possibilities (because such a detail would not have been excluded): that Angels were created either before or after the creation of the earth and mankind.
Your reference to Job 38:4-7 would indicate that it was indeed before. This concept does not conflict with any doctrine I am aware of.  We can also consider that Satan (an angel himself) had already "fallen" and was active in the temptation of Eve and Adam.  Light on Scripture, I know, but God apparently didn't consider that a "need to know" item.