Hi,
A good JHP indeed creates a larger wound cavity and has less chances of over-penetration the FMJ. (JHP are not guaranteed not to over penetrate, and some expand better than others)
However, if one looks at the amount of deaths caused by FMJ's particularly by 9mmp and 0.45, fired from SMG's and pistols in conflicts all over, then FMJ's are definitely deadly.
In South Africa or example, the police carries a 9mm Berreta 92 immitation, and uses only FMJ. it accounts for a couple of BG's almost every single day, many times several in one day.
The most important factors are feed-reliability and shot(s) placement.
The possibility of over-penetration, particularly at short ranges is very real, but I dont think that one is more likely to take chances ans shoot when over-penetration may hit a by-stander when he carries JHP ( I certainly will not take chances).
I think that if all you have is FMJ and they feed reliably (they are more likely to feed well than some JHP's) then you should be fine.
Brgds,
Danny