John Dewey, according to Wikipedia, was "an atheist and a secular humanist in his later life". Paul Tillich was a "Lutheran Protestant theologian". One can expect that there will be differences between them whatever the similarities.
Here is Dewey's use of "supremely devoted" in A Common Faith, page 41-2:
The question narrows itself to this: Are the ideals that move us genuinely ideal or are they ideal only in contrast with our present estate?
The import of the question extends far. It determines the meaning given to the word "God." On one score, the word can only mean a particular Being. On the other score, it denotes the unity of all ideal ends arousing us to desire and actions. Does the unification have a claim upon our attitude and conduct because it is already, apart from us, in realized existence, or because of its own inherent meaning and value? Suppose for the moment that the word "God" means the ideal ends that at a given time and place one acknowledges as having authority over his volition and emotion, the values to which one is supremely devoted, as far as these ends, through imagination, take on unity. If we make this supposition, the issue will stand out clearly in contrast with the doctrines of religion that "God" designates some kind of Being having prior and therefore non-ideal existence.
Compare this with William Wainwright's description of Tillich's ultimate concern:
Paul Tillich believed that the essence of religious attitudes is “ultimate concern.” Ultimate concern is “total.” Its object is experienced as numinous or holy, distinct from all profane and ordinary realities. It is also experienced as overwhelmingly real and valuable—indeed, so real and so valuable that, in comparison, all other things appear empty and worthless. As such, it demands total surrender and promises total fulfillment.
Dewey seems to present God as if God were a "profane and ordinary reality" that one can argue over. Tillich recommends "total surrender". Of course these are just two convenient references, but they suggest that there might be more that is different than similar in their views.
Dewey, J. A Common Faith. 1934. Yale University Press. https://archive.org/details/in.ernet.dli.2015.90386/page/n1
Wainwright, William, "Concepts of God", The Stanford Encyclopedia of Philosophy (Spring 2017 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/spr2017/entries/concepts-god/.
Wikipedia contributors. (2019, March 29). John Dewey. In Wikipedia, The Free Encyclopedia. Retrieved 20:01, April 15, 2019, from https://en.wikipedia.org/w/index.php?title=John_Dewey&oldid=889943494
Wikipedia contributors. (2019, March 6). Paul Tillich. In Wikipedia, The Free Encyclopedia. Retrieved 20:03, April 15, 2019, from https://en.wikipedia.org/w/index.php?title=Paul_Tillich&oldid=886430037