Security and Performance Implications of SQL Tuning Advisor
As long as the developers only have that role in the development database instance, I see no problem; far better to tune now than later.  Now, if your development machine has limited resources, there may be a reason to limit access.  But in general, usually tuning tasks run from a few minutes to the default maximum of 30 minutes; during that time, Oracle may try parallel queries (if enabled), so that could be an issue, but you can play with the instance parameters parallel_adaptive_multi_user and parallel_degree_level to minimize the impact.  

There are no changes between Oracle 11g and 12c that would affect your decision.