We bought tickets through ACV for our trip in August. When I was talking to the person on the phone to buy them, I asked repeatedly if we would get the ticket numbers so we could make fast passes (I don't think she had a clue what I was talking about, even though I spelled out the process several times), and she assured me they came with individual numbers each on their own voucher.
When the email arrived containing the vouchers, they were not the ticket numbers, but rather some kind of order number. I was on the phone to call ACV again and insist they refund me as I repeatedly told the salesperson that I wasn't interested if they couldn't provide the ticket numbers. While I was on hold with ACV, I decided to find out if Disney could help me, so I live chatted and found out it was possible! I quickly hung up with ACV and called Disney and within minutes my tickets were linked to
MDE 
When we get to DisneyWorld, we will still need to collect our physical tickets (actually the kids are already linked to their magic bands), but we can make fast passes!
I decided with our sinking dollar to buy early, the agent wanted to put our trip dates, but again didn't understand the need for the numbers early to make fast passes (they send out the vouchers 30 days before your trip), so I had her put a much earlier date for our trip and agreed that I would deal with the consequences of buying non-refundable tickets (from the moment of purchase) if our plans changed.
When I was speaking to Disney, they said it would depend on how ACV had processed the ticket and issued the voucher as to whether or not they could be linked, but it worked for us (and saved us a bunch of dough!)