Not necessarily early, but it depends on a number of factors.

That weekend is the opener for select Southern Superior tribs on the WI side. The bulk of the fish return in the fall and winter-over in the stream. 6000+ fish returned last fall based on Brule Fishway counts, so those are already there. The Brule gets a smaller run of spring fish which tend to peak around the second week of April, adding to the fall fish.

Many of the fall fish go above Highway 2 which doesn't open until May. So the question becomes locating those fish that stayed below 2. Water temps also play a factor. Seems like the upper Brule warms faster than the lower Brule. You see fish spawning as early as the middle of March sometimes up around B, Stones, Winneboujou etc. When that happens, those fish begin to drop back down through the river. It's not unheard of to catch spawned out fish on the opener. 

If the lower river stays cold, you have to go at it a bit differently than when water temps are above that 38-39 degree range. If you're fishing flies exclusively, sometimes fishing the middle part of the day is more productive at that time since river temps go up and down, and the fish react accordingly, becoming more active in the warmer mid-day water as opposed to hunkering down in deeper pools, etc. If it's cold, you just have to work at a slower pace and really work the water, paying close attention to temps. Not as big of an issue if you are working spawn for instance.