A friend of mine just went through this with her Rott. The ink wasn't the concern but the plastic the pen is made of could be if it's jagged or gets stuck. She watched her dog and it was fine. If this is a concern feeding bread with meals coats the stomach.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD