Will it cause problems?
Almost certainly not, HOWEVER:
The big difference between CJ4 oils and 504/507 blends is the ash (SAPS) content. 1% for CJ4 and 0.6% for 504/507. With the EGR/DPF systems on modern small displacement TDi's, blends are specifically designed to limit carbon build-up (especially in the intake tract.) Also the vast majority of CJ4 oils are Mineral G2 oils, thus tend to have higher NOACK values. All 504/507 oils are synthetic and as a result have higher viscosity indices and lower NOACK.
Higher NOACK values for large Diesel engines are not really an issue, as the sump's are massive 10->20L+ is not uncommon for on-road use (sumps in excess of 100L are common on large stationary engines and mining equipment.) Thus the oil, even in constant high load applications (say a generator or a mining truck hauling up hill) tends to remain cooler than in a small displacement passenger diesels. The large units also tend to have massive oil coolers.
Further more they operate at lower RPM (often
I'm sure there are punters running far worse oils in their VW TDi's, but VW spent a great deal of time, engineering and money ensuring that their engines with the 504/507 spec is the best combination when all things are considered.
I personally use 504/507 Shell Helix Ultra 0W30 in my vehicles (which are not from VW) as it's SN rated and has a VI of >200 with a very low NOACK (can't remember specifically.) It's not that expensive (even in Australia) and is good piece of mind.
Regards
Jordan