Short answer: No.
Keynote does have a feature that allows you to copy and paste styles. It is found under the Format Menu.
Format > Copy Style (Option-Cmd-C) and Format > Paste Style (Option-Cmd-V).
This will even work on part of text within a text box or object fills (it won't change an object's shape, however).
You can only Paste and match style...so that means you have to make a template youare happy with then duplicate and work over it.
Not very good when you have to go back over 16 pags and chane all text etc.
But its great for presentations and animation etc...
if you find a style sheet app, let us all know please.
I've found 'copy and paste style' very unreliable. About the best it can do is copy the text point size and font. It won't bring over the bullet points, and text indent, or the paragraph spacing. Very frustrating.
It would also be very handy if once you've created a new bullet point character, it would be available in the drop down list to use again. Creating a new bullet character isn't very intuitive. I found by trial and error that I could copy one and paste it the bullet dialogue box.
Style sheets, as in InDesign, Quark, Word, wold be a great enhancement.
style sheets in Keynote are called themes, not as sophisticated as in Indesign or Quark but useable
create a new master slide
position and size the box and colour and select font and point size
save the theme
in a new presentation apply the custom theme, then apply the custom slide master
copy text from a document and paste with match style or directly type in to the text box
Themes work well if you are inputting the text afresh.
The problem I've had is when given a Powerpoint presentation and asked to restyle in Keynote. The safest way was to create a new document and put in my background on the master. The text (and sometimes images) are copied in from the Powerpoint document (opened in Keynote), but pasting text attributes from a slide I've already formatted, only applies thte font and size, any leading, indent, style or colour of bullet, doesn't come across. I have to go back to the pre-formatted slide, click on the text bullets and highlight and copy the bullet style from the little window displaying the bullet appearance, go to my imported text, back into the text bullet dialigue box and paste inside the small bullet window.
This works, but it's very time-consuming and seems unrefined.
Keynote excels in maby other ways, with many fancy transitions, but misses the point with styling text.
Adobe Muse copes with paragraph styling, so please Apple why can't you?