Translation:Daenerys admires the invincible Unsullied.
It is actually the comitative collective of zaldrīzes ("dragon"), so literally it means "with all dragons" or "with dragonkind". Given how important dragons are to Valyrians, this usage makes a lot of sense.
Joel above has the answer. I think it's similar to how we say "bulletproof" to mean "invincible", because in our wars being bulletproof was something formidable. For them, being on par with dragons would be a metaphor for invincibility.