Sure, those screws will work. They are comparable to TAPCONs. Here is a video that show a hand poured light weight floor. Sometimes the cement is mixed with foam stuff . . . Strong but light floor found in many applications:
The subfloor will hold the screws but I think your pilot hole should be small, not large. Screw down adequately, to feel, but do not over-drive. Since your new structure is not load bearing, you should be fine.
Dos this help?