In Hugh Fearnley-Whittingstall's river cottage cookbook, he says -and I fully agree- that venison, along with most game, should be minimally marinated in acidic things like lemon or vinegar as it gets pickled, hence tougher. He then makes a case for game being better and softer when braised rather than marinated.
Scottish venison definitely works like above, unless you have a very prime cut or the liver which are better eaten bloody. I would either forget about the curry and eat the prime cut with minimal spices/processes or I would follow the mantra brown-deglaze-braise if I had a stewing cut. It sounds like your curry would be ideal for the latter so why not just do that? Brown the meat in small batches in your dutch oven over very high heat so as not to get the meat boiling - it will stick off the hot surface when it wants to be turned. Then use some neutral alcohol to deglaze (or experiment if you feel like it - I had a beef stew I deglazed with port and south Indian lemon rice worked incredibly well with it!).
Finish with your curry recipe in 120 Celcius for however long it takes for the venison to be melt-in-your-mouth tender (for small size chunks 3-4 hours should be OK).