reverse DNS servfail

[/dev/rob0]

A customer of mine just today got a new ISP. The new IP is 
69.15.253.106. At this time the reverse lookup is failing:
$ host 69.15.253.106
Host 106.253.15.69.in-addr.arpa not found: 2(SERVFAIL)
$ host -tns 253.15.69.in-addr.arpa
Host 253.15.69.in-addr.arpa not found: 2(SERVFAIL)
$ host -tns 15.69.in-addr.arpa
Host 15.69.in-addr.arpa not found: 2(SERVFAIL)

I asked the ISP (cbeyond.net) for RFC 2317, section 5.2, classless rDNS 
delegation: with CNAMEs pointing to PTR records in our forward zone. (I 
do have and can query the PTR's corresponding to my CNAME requests.) The 
customer service people talked to their "DNS engineers" [snicker] who 
told them to tell me:
     "Our DNS Engineers have stated that Cbeyond's DNS service does
      not support this form of classless addressing."
Before I asked, I tested and got NXDOMAIN on this IP. Now it's SERVFAIL.

Before I approach the "DNS engineers" I want to know a bit more.

1. Is there a way to tell if they're running BIND?
    a. If so, why would it "not support" RFC 2317 classless delegation?
    b. If not, can this be true? Maybe in their junkware the in-addr.arpa
       zones are hard-coded to only allow PTR records?
2. Is there a way to tell from the outside why they're getting SERVFAIL?
3. Is anyone else familiar with Cbeyond in particular?

Oh, I looked up another IP in Cbeyond's block, and it wasn't SERVFAIL. 
These are the servers:
$ host -tns 20.15.69.in-addr.arpa
20.15.69.in-addr.arpa name server infinity.cbeyond.net.
20.15.69.in-addr.arpa name server to.cbeyond.net.
20.15.69.in-addr.arpa name server beyond.cbeyond.net.

I don't understand why I can get 20.15.69.in-addr.arpa but I can't get 
15.69.in-addr.arpa.
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