Not really.
Thermal pads contain silicone oil. Silicone oils are excellent electrical insulators and have a good heat-transfer and thermal stability. It can melt silicone products, but those aren't usually in hardware yet. On wetware it has the following effects:
Inhalation - A single exposure may cause the following adverse effects: Headache. Nausea, vomiting.
Central nervous system depression. Drowsiness, dizziness, disorientation, vertigo. Narcotic
effect.
Ingestion - Due to the physical nature of this product, it is unlikely that ingestion will occur. Aspiration
hazard if swallowed. Entry into the lungs following ingestion or vomiting may cause chemical
pneumonitis.
Skin contact - Repeated exposure may cause skin dryness or cracking.
Eye contact - May be slightly irritating to eyes. May cause discomfort.
Pads are used to fill larger gaps between component and heatsink than paste can fill. Make sure to use ones that conduct enough heat and are thick enough to fill the gap without compressing too much (more than 30%). They last about 5 years.