The distribution media you are using does not recognise the hard disk controller by default. You will probably need to use a 'defbootstr' at the boot: prompt to tell it to use a different disk controller driver.
Google for 'defbootstr'
Here's a discussion about the subject as an example:
defbootstr | SCO OpenServer 5.06 - SCO
I don't know whether the driver you require for the ML350g8 is on the media you are using or not, or whether you will need to download the driver and put it on a floppy/USB stick to load it in. Putting the driver name into the defbootstr will either automatically get the copy from the media or, if it's not on there, will ask you to provide it from other media during the boot/install process.
I hope that is of some small help. I'm sure you will get better answers from the SCO experts on here especially jgt when he logs in.
---------- Post updated at 10:32 AM ---------- Previous update was at 10:26 AM ----------
So I don't think that it's the hard disk it's not recognizing, it's the hard disk controller it's not seeing due to lack of driver.
---------- Post updated at 10:43 AM ---------- Previous update was at 10:32 AM ----------
Hey, and also, you should have searched this forum first, I think the answer(s) are already on here:
Installing SCO OpenServer v5.07 on an HP ML350 G5 server
Run a search on THIS FORUM for "defbootstr ML350"