Safe to delete photos on a memory card in the camera?

Is it safe to delete photos on a memory card while it’s in the camera?  Will this raise the probability of file corruption on the card?  Some in our group say it’s completely safe and other feel it’s not a good practice. What’s the answer from SanDisk? How much fragmentation happens when you delete photos and try to reuse the space? Are modern cameras able to effectively track available space, bad blocks and sectors, etc?

These are professional photographers who use these cards daily and heavily. File corruption means loss of income and credibility so this is an important question that needs an answer.