I have seen it done before but like Hornby Dublo 3-rail operates as a two rail system but just happens to use the centre rail as one of the two pick-ups and the motors are designed to run on 12vDC, it is a theoretically simple enough concept to convert it to DCC, that's assuming one wants to convert an entire Hornby Dublo 3-rail layout and is not wanting to mix 2 and 3 rail to run together. The issues happen if one tries to convert something like a Trix Twin system to DCC and that requires some thought, or if one wants to run 2 and 3 rail together.
(I have done this on a DC layout but one had to remove all stock of the Hornby Dublo 3-Rail kind before running anything 2-rail).
But yes. Hornby Dublo 3-Rail has been successfully converted to run on DCC as a complete 3-Rail layout using traditional 3-Rail track.
I hope this helps and is the answer that you are looking for. Somewhere on the internet I have come across such a layout. (I think it was on YouTube).
I will say though that as the current collecting abilities of Hornby Dublo 3-Rail is far superior to 2-Rail, if one wants to convert to DCC for the current collectingability I have to ask "Why?" As carefully cleaning the track (Once cleaned it stays clean way longer than 2-Rail track does if one is talking about itscurrent collecting ability) and adjusting the central tabs and replacing the odd damaged or broken railjoiner is all that is really needed. Apart from track with 20+ years of non-use which obviously will need a clean, other than that it should work find on DC. (Just make sure any old Dublo controllers are thourougly checked over by a qualified electrician before using (The mains wires definately need replacing as are the old rubber type which are way too old to be safe by now however good they may look!) Probably best to use a modern high power controller (Make sure it is one that pushes out over an amp if using ordinary DC as though if properly serviced and have strong magnets they will not draw so much, HD locos do tend to need a decent controller whichnis why I say at least an amp, preferably an amp and a half should be fine for larger layouts.
DCC systems usually push out a good 5 amps for a half decent system so should not be a problem with DCC).
But yes! Can be used with DCC with careful thought to fitting decoders. The only real issue that I can think of is the Dublo class 08 which is a real gem of a loco, but is a bit too internally difficult to convert. Is like opening the bonnet of a Volvo 360GLT or a Peugeot 205 GTI where one opens it and finds it so full of engine that one wonders how one can fit anything else! (And to think the Volvo can't even fit the gearbox under there as the gearbox is at the rear of thr car!). Now that is the Hornby Dublo and Wrenn class 08 for you! Plastic body and yet it weighs as much as if it was entirely made all out of metal! Most other Dublo locos should be relitively easy to convert as far as I am aware though not quite sure of the Castle or the S.R. loco as I never had them. I know the C0-B0 and the class 20 and the Deltic are similar underneath and look almost "Triangy" in their design so are easy. Duchess and A4 and 2-6-4 along with the 0-6-2 should be simple enough (In theory but please check. My Dublo is put away in a box somewhere so I can't check to take a look). I do know they have been converted by DCC'ers, but don't know if they were easy to do. Think it should be do-able with old horse-shoe types as well.
I do prefer nostalgia so for me to consider running them on DCC just does not really tick my boxes as I love the feel of proper switches, but if DCC is what you desire, why not!
But the class 08? When I went all out DCC (2-Rail) in the early 2000's, I went to try and convert all my locos, and while Mainline and Bachmann split chassis locos were a challenge they were do-able with some bodging and some thought. But the Wrenn 08 I had (Same as Dublo in design and they came out in both 2 and 3 rail), I removed the body and looked at the motor and ended up giving up as I would have to dissassemble the thing to even look to find ways to isolate the amazingly solidly engineered motored chassis that these locos are (Probably the most durable 4mm scsle loco ever made!), I just did not even try and put the body back on and sold it to a friend. (I later swapped to have it back when I returned back to DC and the friend had then gone into DCC).
I don't have a clue if the early Dublo ringfield motors can be converted to DCC either, so while 80% of Dublo should be convertable, I am not sure if all of it can.