You would need to work out the Offsets of the splits and then see if the adapters push them out too wide. There are some good web pages that help work it out.
I used PCD adapters on a Mk1 golf to swap to Porsche wheels, they did work but even though they were TUV approved and huncentric they always felt a little out of balance. The Porsche wheels had very little dish so after adding 20mm (IIRC) adapters the ET worked out just fine.
If in doubt maybe find out the width of the PCD adapters, then buy some cheapo Halfords type wheel spacers of the same width and ask the seller if you can carefully offer them up to the car. There is nothing worse than spending a load of money on wheels and have them look odd with too much poke.
The one beauty with splits is obviosuly changing the outer rims to help move the edge in or out but it can all get a bit expensive.
MT motorsport maybe a good person to ask as he has done a fair bit with RS 500 / BBS splits I think.