HD,
Excellent point !
In Canada the AIM states that pilots are "expected" to enter a hold by one of three procedures (direct, parallel or offset). The reason given is "Pilots are expected to adhere to the aircraft entry and holding manoeuvers as described in RAC 10.5, since ATC provides lateral separation in the form of airspace to be protected in relation to the holding procedure."
So, do all the aerobatic manoeuvers you want, but make sure you are following the correct entry procedure while entering the hold :-))
Our AIM gives recognizes a zone of flexibility of five degrees on either side of the sector boundaries for hold entries.
best regards,
Bruce Waddington