If you know someone with experience, give them a call.
Felt tip pens appear to be the best marking instrument for filling in the voting ovals with the least effort. Felt tip pens can be water based or alcohol base. Water based don't bleed as much as alcohol based but in higher humidity conditions, water based doesn't dry as fast as alcohol based. So either may be used. Greg Forsythe tried the Sanford Espresso's a while back, which were an alcohol base that didn't bleed as much, but I believe there was a problem with the pens drying out too quickly.
As well, there is usually no control over what gets used to mark absentee ballots. One of the visible light unit features is the ability to scan a dark mark made by a pen, pencil, felt pen or whatever the voter uses.
Would it be that difficult to program restrictions into the ballot layout program to exclude this situation rather than leaving another potential problem area for the ballot layout programmer to catch?