hardware:IBM X3650 7979-I01

This machine has no floppy disk.

How to load the HBA driver when install openserver 6?

I would try:
See if there is a floppy drive connector on the motherboard, even if one is not installed.
Look for an old PCI ide/floppy controller card, install it and be sure to disable the IDE portion of the controller.
Copy the CD to a Windows system, look at the folder structure for all the 20 or so HBA packages, and add your particular one, then create a new CD.

I'v found out another way to solve this problem.
The new way is to Rebuilding the sco openserver's CD,put the new HBA driver into it.

Can someone tell me how to rebuild the SCO OpenServer CD and to include the latest driver for the IBM x3650 that comes without a floppy drive. Thank you.

I am not sure that you really need to rebuild the install CD, you could just put your HBA files onto a CD. May be take a look at:

How can I create a CD iso HBA from a floppy HBA image?

about how to take the fd images and burn them so that they can be read by the system on CD.

You should consider getting / borrowing a USB floppy drive. Most of the IBM sSeries servers boot from floppy. I have successfully install 3 x3400 last year this way. IBM ServeRAID includes floppy diskette images that with the included utility to write these images to floppy diskettes.