Pakistani troops in Saudi could mean one of three things -
1) The Saudi's have agreed a deal to buy Nuclear weapons from Pakistan and/or have allowed the Pakistanis set up R&D facilities and to provide site security.
However if this were the case then Pakistani troops would be deployed when the weapons are about to be deployed which is likely to take some time as basing, dispersal procedures and methods of deployment would need to be resolved first.
It is doubtful that a sovereign nation would allow foreign troops control and security over their weapons to such a degree. This theory is briefly discussed here -
http://washingtontimes.com/upi-break...5437-7363r.htm
2) The Saudi's have done a deal for the supply of Pakistani troops to be based in Saudi. The only reason for doing this is if the govt can no longer trust its own security forces to any degree to protect it against internal dissent or insurrection.
This would be disturbing in that a nation that must rely on outsiders to protect it against its own populace, is in itself a declaring a weakness which could encourage just such action by "interested" portions of the populace.
Whilst the Pakistanis are Muslim they are still likely to be considered outsiders if/when the balloon goes up and therefore ultimately provocative to the populace. Being forced to rely on non-national troops would in itself be highly corrosive to the legitimacy of the state and counterproductive particularly if they were the only troops under meaningful control.
3) The rumors are all sloblocks and nothing of the sort is going on.
However the fact that such rumours are circulating is certainly suggestive of a loss of confidence in the regime.