The MX record from nslookup tells the address of an MX server. In the email client, this address can actually be entered on both [incoming email server] and [outgoing email server], will this work?
First of all, a MX record is the address of the server handling SMTP for that domain. For example,
$ host -t mx google.com google.com mail is handled by 10
google.com.s9a1.psmtp.com. google.com mail is handled by 10 google.com.s9a2.psmtp.com. google.com mail is handled by 10 google.com.s9b1.psmtp.com. google.com mail is handled by 10 google.com.s9b2.psmtp.com.
The fact that the address can be entered both in incoming/outgoing does not actually mean much. Yes, it does work but nothing prevents that domain's ISP from having different domains all handled by the same host (advertised as MX).
Furthermore, your own ISP might block all traffic going to SMTP servers but his own, in a (futile, anyhow) attempt to reduce spam. Thus you might have to use a different SMTP server, based on where you connect from. And combination of the above.
In short - to answer your question: yes, it might work. But even if it does, it would not mean anything meaningful.