Hi,
It's generally recommended to put a resistor in series between any output and a PICaxe input pin, just in case the input pin gets "accidentally" set as an output. Any value over a few hundred ohms will "protect" the chip(s), but something between 1k and 10k will normally be "best".
If the "pre-built devices" are a commercial product, then it's usually worthwhile to quote the type number, or better a link to their data sheet. Not all "3 volt outputs" are the same and it may help us to tell if you need a pull-down (or pull-up) resistor. But you almost certainly do NOT want a "drop down" (potential divider) resistor directly on the PICaxe input.
Cheers, Alan.