Risks of using ureteral stents when suffering from hypocoagulability (specifically, decreased platelet count)?

Depends on Approach: This would be a contraindication to placing the stents through the skin, kidney, and into the urinary tract - "percutaneous nephroureteral stents" - which is the method used by interventional radiologists. Depending on how low your platelets are, it may also make placing them through the bladder more risky, but your urologist will be the best person to decide.