I've seen some models being tested in NAL's wind tunnel facility with rear grid fins, those seemed like earth penetrators to me. If we are working on such weapons then a Silicon Nitride radomes are the next logical step, this is the only new material we need for such a weapon.
All this is assuming we are making a whole Silicon Nitride based Metal Matrix Composite, preferably a W-Si3N4 based composite. If we are making a Silicon Nitride coating then coating a radome makes no sense. It will bring minimal benefits and will interfere with the guidance and navigation control systems.
You meant this I guess , model of drdo strategic aircraft bomb which is a deep earth penetrator with lattice fins.
Deep earth penetrators are made of super hardened materials , the explosives are at the rear for protection against damage during penetration through progressive layers of reinforced concrete with embedded steel rods , reactive explosive embedded steel plates, granite rock layers etc. Multiple defences artificial and natural are the hallmarks of a HDBT.
What is needed to defeat deep underground complexes is technologies where
1. The vector has the characteristics and power to penetrate deep inside the earth without damaging itself or loosing it's penetration capabilities in the process.
2. The payload of the vector has necessary protection and resilience against damage during impact and subsequent penetration through hardened defences both natural and man-made. Incase of nukes , the design must have protection and safety features to ensure nukes assembly is kept safe and in working condition and no premature detonation takes place due to heavy impact and shocks.
3. Sensors for the vector which can survive impact and penetration rigours while have the sophistication to sense " void " . Void sensing fuzes are required for deep earth penetrators so that the payload is activated inside the underground caverns / complexes for maximum and self propagating damage.
Intelligence driven ops are needed to identify vulnerabilities in HDBTs . Also required are tools that can do topography analysis , terrain analysis , geological analysis , stratigraphy analysis to help find points of vulnerability where correct application of force can lead to over pressure in adjoining areas leading to cave in and collapse of underground caverns.
It is most interesting that India is researching diamond-SiC . Their only utility is very high deformation resistance coupled with very high hardness.
Only single crystal diamonds are known to outperform them in the same .
Even at very high speed impact including hypersonic speeds, the diamond-SiC will not deform beyond acceptable level necessary for penetration through very thick basalt rock layers.
Note : project discription is strategic aircraft bomb
So IMO possibility of it using small sized nuke as warhead is high given the priority of destroying a underground WMD complex with ZERO AMBIGUITY. Conventional explosives effects will be very much localised at site of penetration and probability of desired damage is low in a HDBT.