If your standalone player can play DVD-R DLs, then yes it will play.
Layer Break -
Manufactured DVDs (well, the vast majority) are DLs, also called DVD-9s. At some point in the movie and on the disc (not necessarily the very end of the first layer) the player is instructed to move to layer 2 and continue the movie. In some movies you can tell where this is by the slight (maybe up to 2 sec) pause in playback.
When copying a movie it is preferable to preserve this original layer break, as it is edited so it's in a good place and least noticeable on playback. CloneDVD removes this layer break point completely, so whether it's burned on a +R or -R the movie will change layers at the end of whatever chapter happens to be the last on layer 1.
CloneCD however will preserve the original layer break. If you burn onto a +R the movie will switch layers in the same place as the original.
But due to the structure and formatting of -R DL media every disc has a predefined layer break. No software can change this so all discs and movies will always change layers at the same physical point on the disc.
So to answer the second part of your question, no you don't have to preserve the original layer break. But you'll probably notice the layer change more because it could come in a bad place aesthetically, like in the middle of an action scene or on a jump cut between scenes.
I hope that clears things up for ya.