In general, yes. More specifically, this really depends on the client and situation.
This question is difficult to fully answer without breaking it down more for clairty. For example, by “hot yoga” do you specifically mean the popular Bikram sequence that is often referred to by that name? Are you asking if the temperature is safe? Or are you more generally asking about back pain and yoga?
Regarding the temperature… a great article about heat and yoga can be found here: http://www.acefitness.org/prosourcearticle/3353/ace-sponsored-study-hot-…
The piece basically says that yoga around 90-95 degrees is safe, although Bikram is practiced around 105 degrees and may or may not be (that temperature range was not part of this particular study.)
Heat can help “stiff” clients ease into stretching, but it can take a few weeks to acclimate to increased temperature. A dynamic warm up and working in a room temperature (not air conditioned) space is often enough for most clients.
In terms of the physical poses/sequences for back pain: Many people have reported that yoga helps alleviate low back pain, including the Bikram sequence and other types of Hatha (“exercise”) yoga. However, yoga can certainly injure a client as well. I think good professional practice would be to get medical clearance for a client with LBP before engaging in exercise, and educate the client about “good pain” (stretching muscles) versus “bad pain” (tingling, numbness, stabbing pains) during poses.
I think this answer will also vary with the client’s fitness level. For deconditioned clients with LBP a restorative/”gentle” yoga class is probably a better place to start than a heated, more athletic pose-based class. If by hot yoga you mean Bikram, note that a Bikram class is 90 minutes and quite intense – not great for a deconditioned person’s first yoga experience.
More complex cases would likely benefit from one-on-one attention from a qualified yoga therapist.