if it's safe to eat.

Probably not undiluted:

At 16 billion Scoville units, resiniferatoxin is rather toxic and can inflict chemical burns in minute quantities.

For rats, LD50 through oral ingestion is 148.1 mg/kg. It causes severe burning pain in sub-microgram (less than 1/1,000,000th of a gram) quantities when ingested orally.

Though since it is so potent, it sounds like you can still taste it well below the toxic concentration.

Disclaimer: I am not a doctor or food science expert, and cannot endorse tasting random chemicals with the word "toxin" in their name.