As far as I can tell, you can't transfer Arrival's points into a form that can combine with your UR points. Arrival's points seem to be 100% an internal currency that can be redeemed for cash back- most profitably on travel. UR points, on the other hand, can be transferred into other currencies.

It does seem that they could complement each other, though- use UR points for miles or hotel points when that fits best, and use the Arrival points to pay for travel expenses that can't be covered through a chain (i.e. small hotels/B&Bs) or when it just makes more sense to pay "cash" for a flight.