What Unicode calls the “Unicode line breaking algorithm” (http://unicode.org/reports/tr14/ http://unicode.org/reports/tr14/ see “LB1” to “LB31”) is a method of

What Unicode calls the “Unicode line breaking algorithm” (http://unicode.org/reports/tr14/ http://unicode.org/reports/tr14/ see “LB1” to “LB31”) is a method of determining “break opportunities”, the places where it is allowed to break a line of Unicode text. What the Knuth-Plass paper (http://www.eprg.org/G53DOC/pdfs/knuth-plass-breaking.pdf http://www.eprg.org/G53DOC/pdfs/knuth-plass-breaking.pdf) is about is a method of determining, given a paragraph along with its “break opportunities”, a partition of the paragraph into lines such that (a certain function of) the stretching/shrinking of spaces on the lines is minimized. So yes they can be used together. In fact the Unicode TeX engines like XeTeX and LuaTeX do so (I don't know how well they follow the Unicode specification intrinsically versus with the support of language-specific packages, but they seem to do the job).