Is there a limitation on the number of records that can be added to either the Sender or Recipient Whitelists in the SMSMSE console under Policies -> Whitelists?

There is no limit to the number of users that can be added to the Allowed senders list. However, you should only use the whitelist to allow senders that you have confirmed have experienced false positive spam detection. Do not use the whitelist to preemptively allow all known good senders, as this could open your server up to unwanted spam.

The unfiltered recipients list is limited to 50 entries.