Unsure how that setup would work with hacked pads however in theory if you had a shared ground you may run into issues with needing both devices being active for it to work.
Another solution would be if you had a X-arcade BYOA kit it natively connects to a PC via serial to USB and if you were to use it for a Dreamcast its a simple adapter. I wired mine up today with a DB25 (using serial to DB25 adapters) data switch and have Dreamcast, Xbox, Gamecube and PC all selectible using a switch box. No unplugging, etc... No worrying about grounds, etc.. worth a thought if you arent too far into it.
-Goz