Watch out for policy limitations that might cause issues for a foreign claim. For example, there are about three disability income insurance products in Singapore, but to my knowledge only one of them will pay out claims if the beneficiary happens to be outside Singapore. A LTVP holder has pretty good immigration stability, but I think it's still prudent to anticipate "What if?" scenarios if the LTVP holder has to leave Singapore (upon the death of the LTVP holder's sponsor, for example).
To my knowledge all the Integrated Shield plans are available to foreigners, although the premiums are a bit higher since they don't have base MediShield Life coverage or as many public provider subsidies. However, if you have an Integrated Shield plan already then the LTVP holder should be able to get the same plan, assuming you're happy with yours.