What are your plans/goals? What color is the marble DT? Is it a DTHM or a DTPK? By red, do you mean cherry red or extended red?
If your DT is not a red or not a cambodian, it would be a shame because you will ruin both colors. You see red is very difficult to clean out - like iridescence colors. So if your DT carry irid colors you will have non clean red fry (red with irids).
I kept one of my plakats in a 1.75 gallon kritter keeper for several weeks and he did quite fine. Built nests and everything. For me, it's the length of the tank. He had more room to actually swim in the 1.75g but long kritter than he did in the 3 gallon tall hexagon tank. So I'd say if you find a nice tank that is smaller than 5 gallons and it works for you and the betta, go for it. :)