While hyposalinity works in general well in a HT, it's not a good choice for a DT treatment as you would need to treat for almost 3 months to be safe.
Hyposalinity works by preventing ich to encyst, so if a sterile HT is set up with hyposalinity and the sick fish transferred into it, the treatment can be done within two weeks.
But since already existing cysts are not affected by hyposalinity you have to wait them out - and that can take up to 3 months (possibly more).
Keeping fish for that long at such low salinity can lead to complications and losses.
If it was me I would try to catch as many fish out as possible - usually, with patience you will be able to catch most, if not all fish.
Another good thing about hyposalinity is that newly added fish should not be able to reinfect fish that have already been cleaned up.
The only risk is that you may be dealing with a low salinity ich strain, but that's usually something you find out within a week which usually gives you time to switch to TTM or another ich eradication method.