I occasionally use multiple classes like this and have not had any problems....however, my testing has been a little limited. Marvin, epubreader, a little kindle and ade to name a couple.
I would recommend NOT using conflicting classes though - indent and non-indent - that seems to be asking for issues not to mention slightly bloating the code. I would use classes with different functionality.
For example:
.ctr {text-align:center}
.spacer {margin-top:2em; margin-bottom:2em}
<p class="ctr spacer">
Granted, both of those could be defined in a single class, but it is just an example of not having conflicting styling.
Cheers!