As answered above, LiPo, when charged with an adequate charger (I own the Imax BAC mentioned above) are safe. The ONLY real risk they have compared to NiMH is that you can over discharge them, thus killing the battery (not setting it on fire, just killing it). To prevent that, you can run an alarm, voltage-check them once in a while or just stop firing when the rate of fire drops.
To answer your question about connectors: All battery work on every gun, but they use different connectors. Tamiya and Mini-Tamiya is the standard in the Airsoft world. They are the white-creamy connector that you can see on every airsoft battery.
We use RC technology for our batteries and connectors, but we are late on them. They developed a superior connector called Deans, and we are slowly catching to it. If you want to use it, you can simply cut the existing connector and solder a new one to the wires.
I'm not suggesting you must do this, but it is to explain my point that the connector alone doesn't define the battery.
Also, we really are late, when the RC world considers Deans connector to be old technology, and we still didn't adopted it worldwide.
K3vX | Airsoft Gunsmith/Gun doctor in training.
Feel free to contact me in your preferred language and I'll gladly answer.