It doesn't seem to support it directly. However it does seem to work.
I was just able to fix it. The fix is really stupid too.
So originally the OEM ram was in slots 2+4 from left to right. I added the crucial to slots 1+3. When I encountered the issue, I swapped places with them. The crucial could give 2933 on it's own, but reverted back to 2400 with the OEM back in place. I found a post deep on a dell forum about this where a dell expert suggested putting the dell ram in slots 1+2 and the new ram in slots 3+4. Well I just turned it on and got the 2933mhz I was seeking.
For those finding this post in the future. To explain I was using left to right with the CPU being on the left. On the mobo, it's labelled dimm 3+dimm 1 and dimm 2+dimm 4. You want to put your Dell OEM in slots 3+1 and the aftermarket (Crucial apparently is guaranteed to work) in slots 2+4.