Yes you can custom skin the increment and decrement buttons. Take a look at VScrollBarSkin. The incrementButton uses ScrollBarDownButtonSkin, and decrementButton uses ScrollBarUpButtonSkin. If you open these two files, you'll see the border, fill, path, etc. Copy this skin and simply replace this stuff with your custom image.
I am doing this a different way. Disabled the scrollbar completely and using my own buttons above and below the vgroup
Also going to make a custom 'position' indicator using colour shading to indicate position. Maybe this could be done in skins
but what I like about Flex is the power to create my own controls anyway I want. I always loved ActiveX in VB5 and this is where
I'm coming from. I for sure am enjoying myself learning Flex and taken aback and attracted to the complexity and power it contains.
I'm not sold on XML though.. doing almost everything in pure actionscript.
ps last thing I learned was SSIS and I nearly took off to the land to raise goats after 50 of the damn things
So far so good. One thing I would like to see is a vectorised FXG font that can have all the effects applied you would a vector path.
Apart from that some bug fixes to the builder would be handy but every single IDE I ever worked with has glitches..