Howdy, It could be dangerous for me to help with this but I will give it a try;
Please do not take offense as I will try to be pretty detailed. I do not know what your experience with this stuff is.
Do you know what MAME version of the games your are trying to get this going on? I presume games like Tempest, Arkanoid, etc... (look in your roms folder the rom will either be in Mame172 or Mame106 (AdvMame)).
My HSS image is a couple years old and am sure it has changed some. I have been using several different images actually. Assuming you are wanting to do this on a Windows machine.
If Mame172, you will need to go to the "hidden" partition of the SD card and edit the mame.cfg file. (also referred to as mame.ini file it is the icon that looks like a sheet of paper with a light blue gear on it) See below how to navigate to that folder. May not be as simple as you were probably hoping.
You will want a decent text editor. Notepad++ is what most folks seem to use. I recommend you download that prior to attempting any of this.
You may be asking...how do I access the "hidden" partition... I use a program called Paragon ExtFS to mount the drive. It will show up in the "My Computer" just like your C: drive.. It will assign the partition a drive letter that you can then open. Free version works fine. There are many Youtube vids on how to use it. Download the program...plug your SDcard into the computer and it should assign the Arpicade a drive letter.
Open that. Open the 'home' folder. Open the "pi" folder. Open the Mame172. move to the mame.config file and right click on it. Select "open with...Notepad++ you will then see the full config file where you make the adjustments.
You will need to change the lines below.
1. "multimouse change 0 to 1"
2. Change "dial device to "mouse" (not 100% sure on this...depends how your usb spinner is recognized...hopefully others will proof my work)
#
# CORE INPUT OPTIONS
#
coin_lockout 1
ctrlr
mouse 1
joystick 1
lightgun 0
multikeyboard 0
multimouse 1
steadykey 0
ui_active 0
offscreen_reload 0
joystick_map auto
joystick_deadzone 0.3
joystick_saturation 0.85
natural 0
joystick_contradictory 0
coin_impulse 0
#
# CORE INPUT AUTOMATIC ENABLE OPTIONS
#
paddle_device keyboard
adstick_device keyboard
pedal_device keyboard
dial_device mouse
trackball_device mouse
lightgun_device keyboard
positional_device keyboard
mouse_device mouse
THEN...when you fire up the ArPicade be sure to have a keyboard attached to one of the USB ports...much easier. Lets use Tempest as an example...as long as this ROM is in your Mame172 folder... (first you may just want to test your spinner in Windows as it should move your cursor left/right on the desktop) ALSO...before going to the next step see if it already works in Tempest....If not, proceed.
when you start the game hit the TAB button on the Keyboard. Select "Input(General)" Select Player 1 Controls. Scroll to "Dial Analog" and hit enter. Move the spinner and it should say "Mouse" or "Mouse 1" something like that depending on how many devices you have plugged into the Pi. Hit Enter. Now "Return to Previous Menu."
Now Select "Input this machine). You will scroll down to "Dial Analog" hit enter on the keyboard and move your spinner. You should see it change on your screen to "Mouse 1" or (again...something like that....depending on your other devices hooked up to the Pi. Hit Enter...scroll down to "Return to Previous Menu" hit Enter. Scroll to "Return to Machine" and try the spinner. Hopefully it worked.
I will have to follow up for the AdvMame (106) directions. You need to edit the .rc file. That is a different animal.
Let me know if you need help with that. I sure hope this helps and did not totally confuse the hell out of you.
Good luck!