They should be no worse off than they would be with the betta. Frogs are sluggish hunters since they have very, very poor eyesight. The biggest issue you're probably going to run into is going to be feeding the ADFs--since the shrimp and the betta will probably steal all of their food before they even get a chance to eat. Make sure you come up with an effective feeding strategy and have the proper food to satisfy their needs, or they may starve.
A densely planted tank is always a good idea. All of the inhabitants would benefit from the security and water conditions that plants provide. Keep in mind that bettas are very smart--if they see a shrimp go into a cave, for instance, they will continue to chase it down and root it out. It is inevitable that you will suffer some shrimp losses--if you aren't ok with that prospect, you should consider having just ADFs and shrimp since the ADFs present less of a threat, or just skip the shrimp.
Last edited by Adastra; 09-22-2010 at 04:01 PM.