A release version of an addon will only be for the live version of WoW, however just like you can load out of date addons in live, you can also do so in the PTR provided you copy the addons and their settings over.
At this time I'm unaware of any major API alterations in the 4.3 patch so most addons which function today should continue to function on the PTR with a few exceptions. There are however several base UI alterations to be aware of.
Bags/storage, raid interface, guild interface, reforging interface, minimap, world map, quest tracking, and character portraits received some changes in the 4.3 patch. Addons which alter or are built off of these functions may encounter issues as a result of the alterations. For example, since character portraits were modified, unit frames which display character portraits (particularly the 3d models) may have issues. I say may because it's also possible the alterations won't have an effect though since it is providing more options (and if they are truly optional, default values may still suffice). If you are experiencing issues I would focus on addons which alter one of the above functions as a likely culprit.
Naturally any addon which is zone or content dependent may have issues with any new or altered zones. For example, DBM will likely function however won't have modules for new encounters (unless you download a PTR version). Map addons may also have issues in new zones.
Action bars have not been modified and should continue to function as they do today.
The buff/debuff system is not being altered in this patch so aura monitors should continue to function.
The combat event system is not being altered in this patch so addons which parse combat events should function such as combat text, cooldown monitors, and meters.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.