The military relations between India and Russia is based on "India's needs and Russia's opportunism".
India needs technology and Russia provides it, by selling it. By this Russia gets lot of money, a friend and balance against West(until cold war) and a counterweight to threats from China and Islamist fundamentalits. The new relation(post cold war) is primarily of business interest.
SOURCE (very interesting read): INDO-RUSSIAN MILITARY AND NUCLEAR COOPERATION: IMPLICATIONS FOR U.S. SECURITY INTERESTS
There is certainly a very thin line between civilian nuclear program and nuclear weapons program and most of the times we confuse them with each other.
India has indeed benefited from various nations in her civilian nuclear program which includes US, Canada, France etc. Russia too fits, equally, into this list.
But India has not taken any direct help for her nuclear weapons program from any nation. And, Indo-US nuclear deal is a proof of this. India is the only nation who have not signed NPT and CTBT and still major powers are willing to make nuclear agreements with India and is getting NSG waivers. If India had proliferated its nuclear weapons technology no such things were possible.
Russia did not arm India with nuclear weapons. It was India who armed herself with nuclear weapons as a deterrence to her unfriendly neighbors particularly China. However, India had significantly taken advantage of technology and equipment and nuclear fuel given by other nations for her civilian nuclear program to develop nuclear weapons.
It is a recent (Jan,2003) CIA mid-term report that claims:
Russia has significantly supported in developing India’s nuclear
programmes with technology and equipment, and become a main source of
arms for the country.
Here the 'nuclear program' is civilian nuclear program and 'arms' are non-nuclear arms like tanks, planes and other military hardware.
It also states that this technology and equipment was given to China and Iran too.
The main motivation for this help, as CIA report claims:
Russia’s cash-strapped defence, biotechnology, chemical, aerospace and
nuclear industries, are eager to raise funds via exports and transfers.
for this funds,
Russian President Vladimir Putin in May 2000 amended the
presidential decree on nuclear exports to allow Russia to export
nuclear materials, technology and equipment to countries that do not
have full-scope IAEA safeguards.
So, it is not Russia who is arming India. But its India, who is arming herself as a necessity for national security.
CIA reports: 1. the Dawn and 2. express india
Sublette, Carey. "Origins of Indian nuclear program"
JFK's Overshadowed Crisis