/19 addresses and redundancy

Well, since Sprint is one of the few major ISPs really filtering at the /19
boundary for some addresses(see below), and since this IS their addressing;
you will probably do alright to try to advertise the networks via BGP.
Although I would recommend persuing your own portable addressing, there is
no reason that you should not be allowed to build some resiliency into your
network just because of the networking.

Although some networks have had some issues as times with longer than /19
prefixes, generally you can see from reports such as the CIDR report that
there are plenty of networks out there, in service, that are not being filtered.

Below is what is posted on the NANOG site as far as Sprint's filtering policy:

n the classical "A" space: accept nothing longer than /8
          In the classical "B" space: accept nothing longer than /16
                  in 24/8 space: accept nothing longer than /19
                  in 195/8: accept nothing longer than /19
                  in 206/8 - 223/8: accept nothing longer than /19
                  in 192/8 - 205/8: accept nothing longer than /24
Agis also has a policy statement:

We will filter TWD at /24.
     We will filter 206+ at /19.
     We will filter everything else at /16.
     We will apply next-hop-self to all exchange point peering sessions.
     We expect peers to do likewise and we will route map if necessary.

Again, whether these are adhered to strictly by these two providers, or any
others, will remain to be seen when you give it a try.

Keep persuing your own addressing in the meantime.