There are issues with automatic gain control (AGC) and 802.11g, although I don't know what they are, specifically. An amplifier on fab-corp.com says that it does not include AGC, so it can be used with both 802.11b and 802.11g. The bottom line seems to be to only use an amplifier with signals that it is rated to pass. The issue does not seem to be directly one of DSSS vs. OFDM, but rather one of power levels. If anyone knows more, I'm happy to learn from them.
One thought: if you're using amplifiers on both end of the link, then all is well. If you're using amplifiers to boost the connection to the client, you probably won't get the results you desire. Your clients will see great signal strength throughout the coverage area, but won't be able to associate worth a darn because their tiny little radio doesn't have an equivalent amplifier to boost their signal to levels that can get back to the AP. This is known as the Unbalanced Power Effect (UPE).