Yes, this is where it gets interesting.
I found a few references on the subject:
"Salaries are broken into two categories. The base salary is just that, a base salary that counts toward the salary cap. The second includes all signing and guaranteed bonuses divided over the term of the contract."
http://findarticles.com/p/articles/m.../ai_n19062003/
"The total base salary for the year is the figure used to determine the salary cap amount for each team. "
http://www.chicagonow.com/blogs/chic...#ixzz1BscVv43g
"The Fire's total "guaranteed compensation" for 2010 is $2,890,293.00 although the base salary number is the figure used when determining the total cap dollars used."
http://www.chicagonow.com/blogs/chic...#ixzz1BsdAj4ER
... and if Portland's website is any indication the "minimum salary a senior player can be paid will be $42,000 in 2011, with a maximum salary of $335,000. However, clubs may sign a player for over the league maximum through the use of the Designated Player Rule"
http://www.portlandmls2011.com/news/...aproster-rules
... we could theorize that since DeRo is not a DP and is earning $375k as a base, this is as a result of allocation money. Further, we could speculate that his current cap hit is already at the DP/League maximum of $335k per the above. Clear as mud?
That said, the league doesn't disclose the cap rules and hits like the NHL does. There are a number of factors that could come into play but if we accept the basic premise that the base number is the driving number and bonuses are not factored into the cap (performance, signing, etc.), the cap savings idea becomes really murky.
However, it could lead to creativity in restructuring a contract. Something a higher revenue club like TFC could use to their competitive advantage. Guess that's Mariner's challenge and why knowing the inner workings of the cap was a very important piece of the rebuilding puzzle.