Hello,
I can't see that documented in the current documentation of the probe, but
I found following information on this in earlier documentation.
To specify a custom port on the sqlserver probe you have to do the following.
While configuring the connection on the field ""Server name:"" you have to do the following
127.0.0.1, 5555 (ip/hostname, port)
http://docs.nimsoft.com/prodhelp/en_US/Probes/Catalog/sqlserver/4.7/1941068.png
Please give that a try.
Regards
Holger