I've read every one of these replies and feel kind of sorry for this newbie OP. Walking into this forum asking if old cracked tires can be saved is scary business. EVERY newbie is told to check and change the tires. Help with suggestions for new tires is great because there are many choices out there and some RV's have under rated tires on them. Always use at least load range E.
We have never used the spare, thank goodness, so we updated the old one with a tire that we replaced new. So it is a bit older than 7 years but it is a spare, only for temporary use in an emergency. So you might save by keeping the best of your tires for a spare. Our spare was probably original to the RV, under a cover and looked brand new but we replaced it with a used tire that matched the set we have on it.
Have fun with that RV and use the advice here with a bit of salt. Just because something can happen doesn't mean that it will. On the other hand, be forewarned, almost every awful thing has happened to somebody and it could happen to you! :-)