By refering to Modelsim 10.1c User Manual- Chapter 7, Cell Libraries
, you can find how Modelsim can support various Verilog ASIC and FPGA cell libraries. Unit Delay Mode is explained one page after in the manual.
Concerning VHDL, I can't find a similar section where Modelsim has a confirmed support. However, in Chapter 14, VHDL VITAL SDF
, you can find how to enable timing for VITAL cells only. You can read the following section SDF to VHDL Generic Matching
for more help.
Also have a look at Chapter 6, VITAL Usage and Compliance
on how to make a working setup for VHDL.