Mostly "yes," but some "It depends," would be my response: it depends so much on offensive scheme, personnel, and formation.
In most current offenses, the Y is the TE, and the X is the Split-End. Since almost nobody runs 3-RB offenses anymore, the 3rd WR is usually called the Z, though he could be either a WB/FL in Osborne's offense, a Slot-WR in a 2-Wide, or a do-it-all chess piece in offenses that run multiple formations with the same personnel, e.g. Julian Edelman, Wes Welker, Percy Harvin, Rondale Moore, et al. If you haven't coached or played a lot of football, It's actually a good game-watching strategy for fans to find and follow the Z when trying to understand what went right/wrong on almost any big play. He's the guy who most often goes in motion as he's not lined up on the Line of Scrimmage, and both the QB and OC are watching how defenses line up and match up against him to figure out where their best matchups will be.
The XYZ system came out of the West Coast offense as they almost always lined up in 21 Personnel, which meant 2 RBs and 1 TE. With 5 OL + a QB, that left 2 WRs. If a team kept the 2 RBs but either flexed out the TE or had 2 Split-Ends, it was a bit more complicated, but Y still worked to cover everybody.... But what do we call the 4th guy in a 4-WR formation when we drop a RB? This is where the Duck-R comes in for Frost and Nebraska.
Mouse Davis and the Run-and-Shoot was the first popular offense with 4 WRs and only 1 RB. It was mostly considered a gadget offense, so it didn't really have much effect on the terms and names for any other offenses. It was the rise of Dennis Erickson's single-RB offense in the late 80s and the rise of the Air Raid in the late 90s that made it an almost universal problem for naming that 4th guy, especially when/if he moved around a lot in different formations. If he was usually moving back and forth between TE and a bigger WB who mostly blocked but occasionally caught passes, John Robinson and the Rams had called that guy (Mike Guman) an H, and in some places that stuck when they began sliding him out farther. Since W was the most logical choice to use when added to XYZ--yet I'm not aware of anybody using it--I assume that it was too complicated to use that since we already had a "W" in WR and WB, though it still makes the most sense to me. In offenses that used some 2RB formations and some 4-WR formations, R was used to designate the guy who moved back and forth. I think that this was common in the Pacific Northwest (which is where all but the Air Raid were born), so it makes sense that Chip Kelly at Oregon would call that guy the Duck-R. Since Frost learned it there, it stuck in his offense all of the way until now.
Guys like Wan'Dale and Will Nixon were recruited specifically for that position, though there's no reason why the Duck-R couldn't be a physically bigger player. Faster is always better, but he can be a slightly smaller RB as he'll almost always be teamed up with a bigger RB when he's in the backfield, so the bigger back can do the more traditional FB role while the Duck-R can be the speed back for counters and outside runs. Ideally, the Duck-R is enough of a running threat that defenses keep a LB on the field to help against the run, which makes the ideal mismatch when a LB has to cover him in space as a Slot-WR.
Toure is a Z. Nixon and Alante are Duck-Rs. Rahmir is a RB who can play Duck-R.