Doobs,
It's easier using digital, in may ways. Sensors are inherently sensitive to infrared, and it is usually a nuisance rather than a benefit. The RGB filters mostly pass infrared - even the green and blue ones - so there needs to be another filter over the sensor to stop the infrared radiation but allow the light to pass.
This is not easy to do perfectly at all angles of incidence, so some infrared may get through. It varies from camera to camera. It's rather like light meters - many of them read infrared radiation to some extent, as well as the light that they are meant to read.
Sony 'Nightshot' video cameras allow the filter to be moved out of the way, so that when Nightshot is engaged the filter is out of the way, and infrared sources ("black lights") can be used. The Nightswitch mode also forces the camera to maximum exposure, to deter the use of it during the day - not all clothing is opaque to infrared, and Sony do not like being associated with a device that can 'see through' clothing.
As you have already discovered, some cameras can be used for infrared without modification. You can also have the infrared-reducing filter removed from the sensor, or you can buy a camera with no filter there in the first place - such as the Fuji IS-1. The IS-1 has an electronic viewfinder - which is a useful feature for an infrared camera.
The sensitivity of sensors to infrared has a small downside for colour work. Colour infrared film is only sensitive to infrared in the blue-sensitive layer. Therefore if you cut blue light with a yellow filter the film then has layers sensitive to green, red and infrared. The false colour can then be created from these three (green becomes blue; red becomes green; infrared becomes red). This is not so straightforward with digital, but it can be done.
Best,
Helen