I suspect the motivation for this memo / initiative was research suggesting higher opt-in per incentive offered rates for surveys that do lotteries vs. fixed rewards. E.g., offering $1 to each respondent might get 100 responses and obviously cost $100, but offering $10 to ten lucky respondents might get 200 responses for the same cost.
However, UA management is evidently overlooking the opt-in part. You don't want employees electing to opt in (or not) to job performance.