Energy systems language is definitely still used in systems ecology, ecosystems ecology, and ecological engineering. It can be used in other aspects of ecology depending on the approach of the ecologist, some ecologists appreciate it more than others. For a broad snapshot of how science is currently building upon Odum's 1983 Intro to Systems Ecology, check out a Google Scholar search for the latest papers citing that text by Odum.
In my experience with it, energy systems language and energy flow diagrams introduced by Odum are used as helpful conceptual tools: understanding and organizing complex systems qualitatively and then potentially quantitatively; putting useful constraints and guidelines on brainstorming the effects of adjustments to complex systems; etc. This can be done in a teaching context, helping students understand systems and bridging the fields of engineering and ecology. It can also be done in a high-level professional context, sorting out the intricacies and potential solutions of very complex environmental problems.
I find that energy systems language is used most wherever the study of complexity and ecology intersect. This is especially true in the study of ecological complex adaptive systems and in studying agro-ecology. Even in those cases it depends on the ecologist in question: those with more of an engineering background tend to appreciate Odum's framework, whereas those without an engineering background may rely on other frameworks.