Are the IOS and Android packs absolutely necessary to develop / publish?

If I’m developing a game for Android or IOS, do I really need to have the Android Pro / IOS Pro addons to publish or create a game for those devices?

Yes. The IOS costs $99 and the droid one is free.
To do the droid you must set up the jdk first then the android sdk.
Once this is done you can point to the android location within unity.

No
You just won’t have pro features of those plugins without paying for them.