No they are not. The center section can easily be pushed up and if you are lucky they will get out, if not their head will get stuck and not able to get back in.
The wire racks can be made to work but not easily and should you have a section of heat tape rub through it will let you know the next time someone touches the rack.:rofl:
The plastic shelving from HomeDepot can also be made to work but is also a pain.
Cheapest route is mdf BUT its also the heaviest option and does not do well with moisture coming into contact with it. All my original racks are mdf with lids on the tubs and wheels on the bottom of the racks. Only pain is you have to completely remove the tub to take the lid off. Though I have NEVER had an escape.