For my training I always have a "hills" or "speed" day in there every week. Do you have that in your training? Depending on the distance you are talking about it would be ideal for me to have a trail like that to run on a "hill" day versus the more monotonous way I conquer it. Something called the "hill of death" may be a little too extreme, but there is always walking when you get to that point. I certainly wouldn't use that trail on your long run day, but if the trail is about the same length as the run you'd do on a "hill" day or your easy run day, I'd say go for it. If you are using it for your easy day you may want to consider walking up the hill. It may help break the psychological barrier of "I can't stop running or I'm wussing out" when it's actually better to just get walking.
My first (and only so far) half marathon was on a difficult course and there were several uphill parts, one over a mile long. I had decided at the beginning that I would probably end up walking it unless my heart rate was telling me different. Sure enough, walking up the hill it was, right past people who were continuing to "run" up the hill. All running up the hill for me would have done would have at best kept the same pace, but probably slowed down to the one they were at or worse, while depleting more energy.
Best case scenario it helps build stamina doing a hill day, especially on an actually hilly trail versus on a treadmill or back and forths. Secondarily is that no trail is track flat. Getting used to running with some hills will make what is considered a flat race actually feel flat. Unless you used this trail as your long run and ended up beating yourself up too much, I don't see the downside in using it.