Adding Git-native tags to commits on a repository you'd like to include as a dependency elsewhere doesn't impact dependency importation in CumulusCI for Salesforce.
Only GitHub releases do that. (See sf-cci-02-gh-release-exists-no-sf-package.)
Tags alone are ignored, even if they use the "rel/..." punctuation standard CumulusCI looks for in Git tags associated with GitHub releases.
For more details about building CCI-ready dependencies that will simply build via "latest commit," see sf-cci-01-minimum-viable-build.