All the same rules apply. Nice OTTBs are inexpensive, but generally they require longer time to finish in a discipline as a reclaim than in takes to bring a 3 - 4 year old to the same place. The scenarios mentioned above as my experience both OTTBs and 4 year olds. In general, OTTBs are a riskier value propositions. The first question a prospective buyer is going to ask is 1.) how long has the horse been off the track 2.) when did he last race or 3.) how much training have they had. An answer of 3 - 4 months is going to put off most buyers.
If you're paying board and hauling the horse around to expose it to different situations; you need to be adding $500. A month to it's value to break even. Stop and think how hard that actually is to do.