Romex is a brand name. The type of non-metallic cable for direct burial is UF, the type for dry locations is NM-B. UF is intended to be used with the ends and splices properly sealed or in dry locations. While some code provision might be violated by using the NM-B as installed buried for 24 volt (or less), if it was my property I would use it since it is already installed. If the outer jacket is not damaged, it probably will last for at least 10 years if the cut ends are properly sealed. The voltage involved presents no hazard to most individuals.
No doubt others will have a decidedly different perspective.

Okay that is interesting. What is defined as properly sealed? I'm confused as to how I can hook up these low voltage spotlights to the romex in the first place. I guess I should cut off the "quick connect" plastic boxes on the lights and then just manually splice them to the romex with plastic wire caps and then heavily tape over them?

As I understand it, low voltage isn't polarized so I don't have to worry about which wire I splice into which, correct?

Thanks for the help!!

Ordinary tape will not seal out moisture. This will do the job if you can find it and if it can be sold in your area. The price may be steep. Tape then the sealant on top.

Here is a link that might be useful: Sealant

Anywhere outdoor in conduit is a 'WET' location...and wiring cannot be NM-B in any of such locations.

Period.

Use the romex as a fish line for your LV wire. Pull that through the conduit and be done with a proper installation.