No. In one direction (IIci to IIsi), the hard drive is too large. In the
other direction (IIsi to IIci), there's no way to mount the hard drive in
the box. Your best bet is to get an external drive for the Macintosh IIsi.
There are also physical size and mounting bracket problems with swapping
drives between a Macintosh SE and a Macintosh IIsi.