yes. and no.
crossovers are made to block the frequencies the speakers (made for the passovers) are not meant to play. this is why special (custom) xovers, or the ones that came with them, are to be used.
you shouldnt be able to 'toast' them however (unless your Xovers are made for a lower resistance than the standare 4ohms - or unless the xovers are made for a weird resistance that the matching speakers are set to). given the right wattage with the correct gain settings, you shouldnt have those kinds of problems. but if the xover is made to play lower than your set of speakers can handle at those wattages - you can sure as hell cause some mechanical damage - such as crushing the cone up by hitting the backplate, or jumping the gap - maybe even inverting the cone out.
but more than likely, it will just sound like ***.