Yes, disclose them. The odds of winning a sweepstakes must be stated in the official rules. The accepted form is "Odds of winning depend on the number of eligible entries received" — you don't have to predict the final entry count.
Meet Your Fan shows live entry counts on the campaign page, so fans can see the current odds at any time. Final odds (entries received / prizes awarded) are displayed on the post-draw winner announcement.
For paid entries, "odds per USDC" is often a more useful number than raw odds. Our campaign-owner analytics dashboard surfaces this.