If you want to keep the old (from RPM) Perl around, it probably won't do you any harm to do so, and you'll get all that lovely package management too. The only thing you'll have to look out for are potential nasties from having different perl executables around, but those aren't usually terrible (i.e. you may be puzzled why the script acts differently when run as perl foo.pl and ./foo.pl). I like keeping my RPM database consistent and up to date on my desktop systems, because I think things are just easier that way. On a server, you might want a more DIY approach.
You could (assuming this wouldn't break your Slash install, and I see no reason that it should) nab a perl 5.6 rpm , or nab the source RPM and build it yerself (rpm --rebuild rocks)
Philosophy can be made out of anything. Or less -- Jerry A. Fodor