As title, the description states that you can gamble with them, however the merchant doesn’t show anything apart from the normal inventory.
I’d like to know this as well.
It is not clear.
If you figured out how to gamble, don’t forget to share this strategic information )
Might be a total gamble
Figured it out, when you are revisiting a crucbile where you can start from a higher wave, you can wager the with the dude, you pay more tribute, he spawns more mobs, and you get better rewards.
Loot in crucible generally sucks though, got two legs, one from going 1-100 on the second difficulty, one from 1-50 on the last.
Revisiting the second difficulty and wagering for more spawns, went 50-80, no legs.
Runs take too long and the rewards are shit. Going to hit 150 on the first two difficulties for lolz, then back to Cronley farming 
I got two legendary items on my first run on first difficulty to wave 150. It looks almost as if the last and biggest chest you get, for completing the crucible, pretty much guarantees a legendary. Could have just been lucky. the conqueror chests can also grant legendary items.