They can be. There are many ways to infiltrate offline WAN networks as large organisations like DRDO has.
OWASP has listed some of them here. Read them.
Attacks on the main website for The OWASP Foundation. OWASP is a nonprofit foundation that works to improve the security of software.
owasp.org
Type of CCTV cameras:
IP cameras,
Analog cameras
IP cameras are further divided into
Wired cameras
Wireless cameras
Mode of access:
IP cameras are accessed thru NVRs
Analog cameras are accessed thru DVRs
So unless and until NVR and DVR are connected to
internet, there is no way to get the feed broadcast. Yes, a point of concern are the Wireless cameras which is a fashion now-a-days.
Now for someone to patch into your feed, he has to get access to your camera or NVR/DVR in person or digitally. So if you have a robust security policy in place, accessing them is impossible in both the ways.
But why this concern has been flagged for Chinese equipment if that's the case?
Let me give you a simple example. Once one of our client whose IPVS was based on X, forgot the password for one of his Hikvision camera. So to reset the camera when he approached the customer care, they asked him to give internet access to it. So within a week, they floated a new tender and replaced the whole IPVS setup. Now this client was not even under MoD or MHA, but they have red flagged the issue.
As far as security policy regarding hardware installation and replacement is concerned, all the uniformed or un-uniformed services have a robust policy in place. The real concern for them is not the Chinese CCTV cameras, but the mobiles, which they can't control per se.
So don't get excited about everything you see or read.