Yes, I am sure that they are sensitive to oxidation. You haven't given any ref for this article, and although JMC is a good journal, you can't always believe what is published.
The synthesis of these compounds is not practically feasible anyway. You have to start with a o-Diaminobenzene, which are incredibly toxic and carcinogenic, and react that in Et2O with Piperidinyl Sulphur Chloride. Here is the ref:
J. Chem. Soc., Perkin Trans. 1, (11), 2591-3; 1984