Ah, just figured it out. The system Java, in this case java-1.7.0-openjdk, conflicted with the JRE installed during WFA installation (jre1.8.0_144). Apparenlty the new JRE doesn't get set properly with /etc/alternatives.
At any rate, here's the fix.
# yum remove java-1.7.0-openjdk\*
# yum remove wfa
Then reinstall and see this.
Setting WFA license key.
Key was set successfully
No error pop-up after logging in.