Applies to all types of elastomers. Regular petroleum based grease contains oil and a thickening agent. Many hoses and rubber parts under the hood are made of EPDM rubber or sometimes even SBR rubber. Neither of these is oil resistant and will swell and even crack if allowed to absorb oil. Cooling system hoses, for example, are typically made from EPDM. Typical oil resistant parts mad of rubber are made of nitrile rubber; these include things like hydraulic hoses. Very high performance/high cost silicone based elastomers are also oil resistant.
Silicone grease is a polymeric material (perhaps with a bit of silicone oil added)that will not absorb into rubber. It will generally stay on the surface and therefore it can lubricate but not penetrate the rubber part. As such, it is ideal for lubricating the surface of any rubber part. It wl not cause swelling or cracking.