...if Tri-jets such as a Falcon 7X or a MD11 is subject to Single Engine climb gradients if only one engine fails during takeoff?
All perf A aircraft (with 2,3 or 4 engines) have to plan on having one engine fail on take off.
In the case of the TriStar (L1011) on take off from LGW 26L, we had to "swing the cone" (15 degrees left turn with 15 degrees bank - to avoid Russ Hill) with an engine failure.
If we were light, we could do a single engine GA (with 2 engines failed) from about 1500 feet on the approach by descending on the glide path whist accelerating to enable a clean wing then "climb" away (more of a limp really).