To be clear... "Jive" does not have a rich text editor - it adds on TinyMCE, and my bet is that ASC's AppleJiveWare does NOT have the latest-greatest version of Jive much less that of TinyMCE's "Premium" version within

TinyMCE | Features for WYSIWYG HTML Editing
https://www.tinymce.com/features/
I do not recall speel-chicker failing with any regularity here. If I *did* experience it, I would likely not worry much - OR - restart the browser
My best guess is that the "browser's" speel-chicker is what we all see here when editing - not Jive/TinyMCE.
Firefox automatically checks the spelling of words that you enter in text boxes containing more than one line. As soon as you finish typing a word, it is checked against the words in the installed dictionary. If the word is not found in the dictionary, it will be underlined in red, as in the following example:
[above emphasis is mine]
How do I use the Firefox spell checker? | Firefox Help
https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker
Thus my trubble-shouting step of trying different browser(s) 😉
Again, a best guess is that OS speel-chicker has nothing to do with the OP's issue 😎
added
OR... Safari relies upon OS X speeling dikshunary (???)